I own an Inspiration and a Sidekick. And have for a lot more ccr's a user level cert. Also have, I think a lot of hours on a CCR to know a lot about things that can happen.
I use a DSV on both units. I have tried a BOV on the Inspiration, but I found it too bulky and too heavy, even if they say it is neutral in the water. When you use a scooter or there is current for sure you will bite harder to hold it in your mouth. So I prefer a DSV.
But there is nothing wrong with a bov. The only thing is: don't expect the 3 liter is a real bailout. So you still need to take at least 1 extra cylinder for bailout. I know that there is said till 20m with a 3 liter tank you don't need to carry a bailout and that this is done quite a lot of times. But then it starts with some problems. If you have been to 20m, go up to 12, go down again to 20m because you are on a nice reef or wreck, maybe you have used more diluent than expected.
I have drained a diluent during a 4 hour cave dive where the max depth was only 20m. So I had to plug in my bo as offboard diluent. Yes, this was a technical dive and not a recreational dive, but in stressfull situations, only 600 liter gas is not a lot.
Another point of taking no real bo with you is that you have 180 bars left, Oh, enough. Then next dive you have 150 left, still enough. I can do an easy dive to 20m with only 50 or 60 bars left in my diluent cylinder and don't worry about it. I always carry a real bo. So can plug this in as offboard diluent. But if you don't have this, and you need a real bailout, the bov will only give you a few breaths.
So always remember this if you decided to go for a bov.
There is no redundancy for complacency.
Then the HUD. My sidekick does not have a hud. I only have a shearwater on it for the PO2 readings. I have done a lot of cavedives with this unit and it is also my bo ccr. Is the hud requied? No, it is not required. But it has some big big advantages. And also here it comes to complacency and lazyness of the human being.
In a ccr course there will be told that you have to check your PO2 every 1-4 minutes. Great. Normally your PO2 will not be too low in the, let's say 4 minutes (You also do a skill where you swim at constant depth with a starting PO2 of 1 to 1.3 and let it drop to 0.7 to let you know that this takes a long time.)
But if you are enjoying your dive, or are doing a skill like using a reel or fighting against current, do you know the time? If you do a skill or fighting against current, probably your O2 consumption will rise. Normally still not that you have a problem within these 4 minutes, but what if you forget to check and it will be 5 minutes? Or 10 minutes? A blinking light for a HUD is enough. If this turns from green to red like on the Inspiration, you will see this for sure.
If a hud has just 1 color and the cadance it is blinking tells you the PO2, you have to count and this does not work for everybody. But a changing color will be seen by most people (if you are not colorblind, then the position of the lights is important or the way of blinking).
So you must always be aware and be extra aware if you don't have a HUD.
Also the other side, a too high PO2, a Hud will help you with. I have had a divecenter that filled my diluent cylinder on purpose (because they believed in EAN and the price for air or EAN was the same) with EAN32 when I asked for air. They did not tell me. And I did not check (wrong, I know, so now I check also airfills. We are all human and I don't lie abouth things I did wrong, even instructors can do things wrong as they are also human). So I had my PO2 in the right range and then went into a cave. The first 900m where quite shallow, and then it went to 45m. I saw the PO2 rising, flushed my diluent, but it was still not getting down. At that moment I realised it was the diluent and after the dive I analysed and of course went back to the shop to ask what the hell they did, they told me they had a DIR phylosophy and then EAN is a better gas, but they did not know anything from CCR diving). A HUD shows in this case if the PO2 get's too high. I always check my PO2 when getting down, so then I did not needed the HUD, but it can be a great help if you are distracted for some reason.
I also had 1 time that I could not clear my ears. We had been diving a very long time at 24m and then after more than 90 minutes we decided to go to 43, another tunnel in that slatemine. Around 32m I could not clear my ears which is very very strange to me. So I decided to cross my arms, take my nose and try to do a vasalva. Because I crossed my arms, my elbows hitted the MAV of the oxygen. So I was blowing pure oxygen in the loop while trying to clear my ears. I saw this, so could handle it and do a diluent flush. But the PO2 in the loop went very soon to 2.2. Also not directly a problem and you learn how to handle such things, but the HUD can be a good warner for such things if you don't look at the handset if this is needed.
I can also tell about people who forgot their flowstop, so did not open the oxygen, and then walked with a loop in their mouth to the water. Did fins on, and then the hud started blinking because of a low PO2. If you did not see the HUD, would the PO2 drop too low? There is a chance this happens.
So the HUD is optional, and I have decided not to put one on my Sidekick yet. But you must know for sure that a HUD has a lot of advantages.
For your first ccr I would look for a unit that has a HUD.
If I need to choose between a BOV as nice to have or a HUD, I would spent my money on a hud.
A tempstik or CO2 sensor are nice to haves and lower on the list than a HUD for me. I have had a CO2 hit were my tempstik did not warn me, and I have seen a lot of problems with a CO2 sensor not working.
