First thanks for all the comments. I'm sorry for not posting earlier. I'm still away and don't really use my phone or go online on holiday. But it's monsoon rains today and I'm taking a break from studying.
Here's an update as to where I'm at. Sorry wandering and disjointed. I'm typing on a phone:
1) decided first to learn Sidemount prior to any tech course. Kind of an intro to tech anyway. Definitely recommend this as a first step. I'd be at a huge disadvantage starting a tech course eg. Advanced nitrox or Padi Tec without doing some kind of twin tank configuration course first. I feel I'd have been unable to focus on new information as I'd be grappling with new equipment instead of listening and learning about new gas mixes, protocols and deco procedures.
2) Having now certified Sidemount (TDI) and done 6 dives, I feel very comfortable with the new configuration and frankly could not have imagined the increased safety and self-reliance that Sidemount (and in some ways backmount but not starting that debate!) brings. Very happy with all that I learned. Like anything, experience will provide the real training. I feel my buoyancy/trim has improved a great deal and I understand all the drills, skills and reasons for them.
3) I was at 20m when completely unawares, my instructor fully depressed my LPI inflator while simultaneously dumping air from the back of the bladder. I happened to be on my left short hose at the time. Unlike other exercises, this scenario was not discussed prior and due to poor visibility and my instructor coming from behind after helping another student who was staging a tank, I was genuinely reacting to an 'emergency'. I was pleased that I was thinking clearly and knew how to assess the situation. I was grappling for the right hose clip to be sure I knew the reg was there, before... and with the other hand, closing the left cylinder. Please understand that clipping on/off and retrieving a wayward long hose was/is not second nature yet. I'm working with my cortex not my cerebellum as it were. So I wanted to check. My life after all. I then breathed down the left hose, to check it was off. The gas loss stopped. And I changed regs. All while maintaining depth, position and even trim. For good measure the instructor took off my mask while I was closing the left tank and I were lenses and had to close my eyes to put on spare mask. He said after he was simulating me hitting a sharp bit of a wreck that cut the hose and in panic knocked my mask off. In debrief he said I did good job but that I should not have felt for the right reg clip before turning off the left cylinder. That the priority is to stop the gas loss. This exercise really has cemented somehow the importance and benefits of independent tanks. I guess in the real world at 20m in poor visibility, I wanted to take that extra 2-3 seconds but I knew I had a whole spare tank.i never before appreciated the independence of two tank. I presumed it was all about extra gas or different mixes rather than redundancy. Was a very important real life lesson. I found the course very educational and exciting to learn.
4) I chose TDI as the agency after meeting 4 instructors and asking them questions that other posters suggested. Best question answered by all was why they teach and I got sincere and thoughtful answers; and do they play at a higher level than they teach. All instructors did. All but one dived beyond 100m on multiple gases and regularly used a rebreather as well as multiple tank configurations. All taught TDI and PADI and all said I should go with TDI out of the two. Don't know why? Id say PADI has it right from explaining to a consumer what the course progression is. But I was being snobby if I'm truthful. PADI (probably wrongly) feels like the mass-market newbie people. Spose there's a cool factor. TDI and BSAC 'feel' more cool. GUE, which I'm rapidly realising is a great system with great instructor following was mentioned by one instructor but the other student at that school wanted to do TDI so it wasn't a viable option. I note from several posts on the thread that GUE would take longer to advance to deco. Although I'm very keen on the theory and taking it safe, I do want to progress. So I'm happy with TDI and the course / instructor I'm with.
One consideration on choosing a school or instructor (that is to a great extent agency independent) which I don't think was mentioned was the equipment available. It's only relevant to me thinking back. All but one school had X-Deep harnesses for Sidemount. Given I'd be renting tech equipment wherever I go to dive for the next 30 or so practice dives, it is something I was pleased to know I was using 'standard' kit which I knew how to adjust by myself. For your info, I also used jubilee/snap-bolt as the tank to harness connection. I however was trained on another popular method of connection.
5) as my objective in diving, apart from enjoying the doing, is usually video graph of landscapes and wildlife, I took my camera setup on 2 training dives so I could practice having that extra stuff with me while with an instructor. I actually found that apart from the spg checking and reg switching which obviously required free hands and more maneuvering than Rec single tank setup, my camera operation was as normal. I think it's actually easier on Sidemount to hover. I seemed to have a problem with buoyancy towards the end of the first two dives due to setup and the extra empty tank and wetsuit that I usually do not wear but one extra weight resolved it. I was a little head heavy but changed to heavier tech fins from my personal aquavanti fins and that resolved that.
6) On our last dive we were very shallow with 8m seabed for last 20 mins doing skills, so not foolhardy by the instructor (even though down to 35 and 45 bar), but we did what is my longest ever dive at 107 mins with 15m max depth. Sidemount is bl*ody awesome. Biggest feeling is I feel safer. And feel if needed I could look after myself and be more self-reliant. Always worried on single tank out in Thailand what newbie OW diver you get buddied with who has no experience and wanders off. *Loved* that tech protocol demands two of everything and the seriousness with which tech trained divers take things. The s-drill and start procedures at 5m make sense. The importance of diving the plan and really sticking to depths agreed prior. It so easy these days to just rely on the computer. Nice to get back to basics a little. And feel proud to join this tech community. Felt very welcomed by instructor and school. Was with another modestly experienced diver (like myself) and was treated and taught with respect. I will try to be a good asset to my team and continue to study, practise and learn. Can't wait to learn how to explore caves.
7) started a combined advanced nitrox and decompression procedures combined course which I'm in the middle of right now. Fascinating stuff. Love all the equations. I studied physiology at university so it ticks a lot of that innate interest. I'm geeking out on the history of bubble algorithms!! Ps. New instructor just for variety to see different styles and already picked up new tips eg. Tarts instead or Start which I think is better/more practical. I don't give people's names in posts (to protect the innocent!) but in case any details are picked up by people reading, I felt my first instructor was excellent and this instructor change is no reflection on him and mainly was a location change thing.
I will be doing my first planned deco dive in next couple of days. Learned a huge amount in theory already and feel safe given the brilliant protocols developed from lessons learned by the generations of 'tech' divers before me.
Will give final report on the rest of the course when I return.
