Reading between the lines the problem isn't so much your gear as it is a lack of practice. -- I have no doubt that I need more practice! -- For example, you say when you dump air you're high, then you crash down. To me that sounds more like you're too heavy and are managing too big of an air bubble in the BC than it is a fault with the dumping. -- I see your point, and in fact, this problem really came out the other day when I forgot to reduce my weight for the second dive (with my tank) after having added weight for the first dive (with a rental tank). --
You say you flip over if you relax, sounds more like a trim problem than anything else. -- Well, yeah, I do have a trim problem, and I've been working on it. But this BC doesn't have any trim weight pockets. -- Can't feel the Velcro on the pockets, sigh, I dive a BP/W and don't have pockets to feel except on my leg. -- Yeah, I think I may have better luck with a BP/W (or maybe a back-inflate BC) and pockets on my suit, too. -- You also mention it moved around on you before you modified it, to me that sounds like it didn't really fit you in the first place and may be too large for you. -- Well, not being an expert, and having to rely on others (like the guy at the shop who helped me pick out this BC), and not even remembering if this model even comes in different sizes, all I can say is, "I'm pretty darn sure that, for this model, the size I have is the best one for me." -- The squeeze you feel is common with many jacket BC's and to be honest you may bind a back inflate BC of some type more relaxing. -- That's what I think, too. --
You also said you can't find the dumps easily and can't get the knob in your hand when you do. Frankly that's a matter of diving it more and getting used to it. -- Fair enough. I think you're right on this one. -- Some people don't even have a knob, they remove it and have only a string left so there's less entanglement risk. (Not me though).
Here's what I think you need to do, first if you don't like the air2 replace it. That's cheap enough. Second, figure out if the BC really is the correct size for you. If it is then dive in it more often, wear it around the house and find the dumps in the dark. Really you only need one, find your favorite and use it only. Try the bottom dump on it for practice. Forget about the others. Use the hose if you want to when you're more upright, bottom when you're horizontal. Get your trim right, sounds like you have a couple issues here. First find out how much weight you need to be neutral with an empty (500 psi) tank. Now find out where it needs to be to get your trim right. Place it on a belt, if your feet drop move some of it up and vice versa. You'll probably find you don't need as much on the belt as you have and some of it will be up higher on your body. Place it on your tank straps if you need to. Be sure to balance the weight side to side or you will roll over when relaxed. Get it right and you won't. The steel tank up top will only roll you if you start to roll in the first place due to being out of trim. -- Here's what I don't understand: by this argument, there is no truly neutral trim. You are always "riding the bubble" to keep from flipping over. As soon as you get off-center, you flip over. Now, maybe I'm naive, but I have the feeling that perhaps it's possible to achieve a situation where your weights are close enough to your center of gravity where that doesn't happen, and you're able to maintain just about any position without a lot of effort. Maybe I'm wrong --
You'll find it may take you 10 or more dives to get the trim right, when I used a jacket BC it took me 20 dives to finally be happy with my trim. I'd move weights around every dive in small amounts. Finally got it right. It took me 2 dives to get my trim right with a BP/W because the weight was already up high over my lungs and not down low on my hips making me feet low. -- This paragraph seems to support my argument. --
There is nothing inherently wrong with your gear given the attention to detail it needs to be right. -- I disagree. I think a jacket-style BC is inherently wrong for me. --
I'm making a lot of jumps here, assuming things you haven't said and I may be way off base. I'll ask you this, when you quit moving where do your feet go? Can you stop all movement and just hang motionless or are you pulled in some directions, and which way? -- If I relax, stop swimming forward, and just go limp, I end up in a position with the bottom of my tank at the lowest point and my feet just a little higher than my head, like I'm sitting in a hammock. -- At your stops, can you easily hold 20 feet? -- I've been using a little less weight every time, and have gotten it down to 16 lbs, and had no problem staying at 15' with 500 PSI. Now, I wasn't totally relaxed, because I was maintaining a prone attitude, but I wasn't fighting to maintain depth. -- How about 3 feet? -- Never tried that. -- On an empty tank? When you kick and glide, do you stay at the same depth or do you tend to go deeper during the glide or shallower? Where is your head? -- Up my... oh, sorry, TOS and all! -- Is it up down or neutral?
To be honest, I think you'll find if your BC fits properly you can get it to where you like it just fine. PS, if you're weighted right the squeeze should not be that tight.