Personally, I do not recommend the adjustable harnesses. I bought my OMS plate with the Smart Stream harness linked above. It worked OK, but I ended up throwing it away and switching to a single-piece harness. I found that the adjustability was not very helpful, and in order to get the waistband tight enough, I had to also over-tighten the shoulder straps a lot. Not ideal.
The thing is, as shown in the video from
@happy-diver a few posts back, shoulder straps simply don't need to be tight. There should be an extra four inches of slack in there, so a little +/- from different exposure gear doesn't mean much to me. So, you do not need to adjust the shoulder straps for warm water and cold water diving, just leave them loose. And the waistbelt, of course, is already adjustable.
The only thing you need to adjust is the crotch strap length. I have shown up a few times at a warm water dive site and realized that my crotch strap is still adjusted long for cold water. I just twisted it once or twice to take up some length, and splashed that way. Then, adjusted it an inch or so during the surface interval. If I ever show up at a cold water dive site and it's too short, I would take the time to loosen it -- time spent faffing around in the local parking lot isn't very expensive, so my buddies wouldn't mind waiting a couple minutes.