To me, the most important features of a BC are that it has to fit, and fit well, and hold the tank stable, and it has to have adequate but not excessive lift for the purpose. It has to vent easily, and have some attachment points to help keep gear tidy.
I clip very little to my BC, except my pressure gauge and my lighthead and primary reg when they are not being used. Anything you clip to you runs the risk of being lost, and also the risk of getting tangled up if you dive near kelp or weeds, or anywhere where there's fishing line or navigational line. Putting stuff in pockets keeps it much more secure, and streamlines you. At any rate, I've found 4 d-rings to be more than adequate, even for tech and cave diving. (Yeah, you need the 5th on the crotch strap for the scooter . . .

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The beauties of a backplate system are that you can configure it to match what you are doing, and if what you are doing changes with time, you can adapt it easily. I have, for example, a 17 lb tropical singles wing, a 30 lb cold water singles wing, and 40 lb doubles wing -- but they all fit on the same backplate, if I want them to. (Of course, being a gear junkie, I have different backplates for different applications as well, but you don't HAVE to do that.)
A backplate rig comes apart as far as you want to take it. It's easy to take the wing off and roll it up, and to take the cambands off, and then you just have the plate and the attached harness, which packs up pretty flat. A light (Al or Kydex) backplate may weigh less than a standard BC, too, by a couple of pounds.
For cold water divers, the advantage of having a stainless plate become part of your ballast is very nice. It puts weight up on your shoulders, where it helps you stay horizontal, and typically eliminates a couple of pounds of weight you had to carry to sink the padding in a traditional BC.
There are some very reasonable BCs out there -- my husband dives a Balance sometimes, and likes it a lot (but he dives his BP/W more). I have a little pink and black jacket BC that I use in the pool with students, and it fits me very well and keeps the small tank I use in the pool stable -- but I think I'd miss my crotch strap a lot if I tried to use it with the heavy steels I use in Puget Sound.
The really important thing is fit and stability, and as the OP observed, it's very difficult to evaluate those things when walking around in a shop, particularly without your exposure protection, and without a tank in the cambands.