Sure, essential skills like buoyancy, trim, and propulsion are definitely required before progressing down the tech road. They are great examples of essential skill mastery. The problem wit the SDI/TDI (and really almost every OW sidemount vs. the tech component) is that they just straight up skip what most people would consider essential skills in the OW component because they assume either A) the student doesn't need to know it, or B) it's too difficult for the student to do it. The problem is that neither are true.
A good example is stowing the long hose after air sharing. Most OW sidemount courses say, "hey, we're surfacing, don't worry about it!" The problem is, without teaching you to stow the long hose underwater, if you're ever in that situation, you're screwed. I can see several situations even in open water where that skill would be required.
Look at it this way, you're not losing anything by doing the TDI component. However, by doing the SDI component first, then the TDI component, you're really only adding an additional fraction of information to what's already been presented in the first course. I don't specifically know the SDI/TDI course material, but with some other agencies the information is even contradictory when you progress. My position is that you should be getting the correct, complete information from the get go. They're the same book for a reason, so why wouldn't you take advantage of getting all of the available information, rather than paying for a top up on stuff you should already have. Or worse, having to re-learn skills because the OW and tech components contradict each other.
A large part of technical diving is optimization of gear and procedure. I think this is apparent enough in the way people learn to recreational dive vs people starting down the tech road. So why not start with the optimized procedures and gear from the start? More and more people are seeing this as a better path to take, evidenced by the increasing popularity of BP/W's, primary donate, etc. Why go back to the "stab jacket, face covering, golden triangle" of the rec sidemount world when you can immediately start with the "long hose, in trim, BP/W" of the tech sidemount world.
It was very helpful and rather neat to be able to see myself "live" rather than in pics and video after the fact. I *love* SM. It was wonderfully stable and comfortable. Started out with my new Deep 6 fins. But the new fins on top of SM was just too much new stuff at once. Went back to my splits.
