So a few more comments and questions.
1) very important. How easy is it to get into a BP/W while in the water?
I can give you my perspective. I've used two different bp/w rigs: One Halcyon Eclipse (rental) and one DSS (mine). Both have the most basic harness, with no additional clips or ez-in type things. I wondered at first, because I had taken my first OW class (years ago) in a vest BC with full Fastex buckles, etc. And here I was in OW class again (had gone four years and only made two dives since first OW class so re-took it), with the only bp/w and never having put it on before that day. But it went fine. Doff and don actually seemed easier than I remembered - maybe because the straps are a bit "stiff" and tend to stay "open" so you can slip your arm in? I don't know but it seemed fine (also note that you don't set up the shoulder straps to be "tight" as they don't need to be).
Then I got my own rig and again, all seemed fine.
But then, last February, I totally wrecked my shoulder. And on top of the injury I got "frozen shoulder." I couldn't even comb my own hair and put it in a ponytail, and getting things like coats on and off was murder.
By June I REALLY wanted to go diving. I figured I might have to put a buckle in my harness webbing because my mobility was still pretty bad. I decided to just bring the buckle(s) and my sewing kit along, and see how it went. I did loosen the shoulder straps (symmetrically) a bit more than usual. The first day I rented a tank from the shop and just got into a nearby canal along with my BC (not on me) and then tried donning, doffing, and "diving." It worked okay - actually easier than I thought it might - and so the next day... real boat diving!
The whole first week I jumped into the water with just my mask, fins, and weight belt on (2# so not dangerous), and then donned my rig in the water. The only problem I had was sometimes the free end of the waist strap would get behind me or the crotch strap would get behind me and they would be hard to reach. My buddy gave me a hand (it would not have been hard for me if I had not had lack of mobility on that side). At the end of the dive, I then doffed my rig in the water and got aboard. Again it went fine.
The second week I "graduated" to donning my rig aboard and jumping in fully clad, but I still doffed in the water and handed up. I'm just mentioning this because it was a lot more situations of "imperfect" conditions vs. just doing it sitting on a boat bench.
So I never did put a buckle in, and it wasn't a problem even with one "bad wing." I had the shoulder straps a bit looser than usual, but not a lot. The rig was still not moving around on me while diving (I hate that). That's not to say everyone would have the same experience, but just to give you my perspective.
Since I have yet to see one/ or try one on first hand, it is kind of hard to imagine how you put it on. if I clip it on like a BCD then OK if I have to step into it and then tighter straps, that could be hard floating around in the water.
What I found was that yes, if the rig was floating, it was difficult. I would simply let a bit of air out of the wing, so that it would start to sink (but only slightly) and then it would be right "there" and not hard to slip into.
What I do (same on the boat) is let my arms slide down into the shoulder straps. That's vs. reaching way back with them like I would to put on a coat. Then I pick up the crotch strap, feed the waist strap through it, and buckle it up. Then I'm in. Once you have the straps set (which I only change if I'm going from no wetsuit to wetsuit, or have a shoulder injury) then there is no adjusting when you don the rig - you just get in and buckle it up (the tightness of the waist band you do control each time, like fastening a belt on a pair of pants).
2) I really do not want to wear a weight belt. That was is my number one complaint with the diving I have done so far. I just find it very very uncomfortable. So where do I put the ditchable weight? Is there flexible wieghts something that would mold itself to you, I.E. sand like?
There are "soft weights" which are essentially like bean bag pouches with lead "beans." I like a weight belt - and it can be nice to have weight off the BC - but in the keys in summer diving (which you mentioned you are planning to do for starters) you probably will not have an issue with putting some weights right on your BC. You may not even need any if you have a steel backplate, but if you do you could put pouches on the waist band or on your cam bands (depending on where you need it for trim).
So far my wife does like the idea of a BCD,
Just a note: BP/W, back-inflates, and vests are all "BC's" It's only if you dive without any sort of inflatable buoyancy compensation that you are not using a BC (which you probably would not do at first).
She like's the idea of feeling secure in a jacket. However the jacket that she likes so far (Mares Hybred) is pricey and that combined with the slight more that we are spending on the Regs, makes things higher that I wanted to budget. I do not see her really out growing it.
For myself, in the grand scheme of things, the BC being one I like is so important that I would spend whatever it took (obviously not thousands, but within reason) to get one I liked and that fit well. That said, is she sure she would like it in the water vs. on land (where they seem to have features that would be wonderful for backpacking but maybe end up being not so useful in the water?)
No vest BC's fit me well, so I can't relate on that angle (except that I disliked diving until I had a BC that did fit). I will say that I, personally, feel more comfortable in my BP/W than I did in vests, but maybe that's because they didn't fit me well. On me the tank slopped around a lot with them, and I felt all bunched up under the arms.
I guess what I'm trying to say is that if your wife really would like the Mares best, then, if I were her, I would get it for sure. If she's not sure.... then it would of course seem like a lot of money spent for something less than ideal.
Blue Sparkle
PS: One last note:
I wonder if she would like a cheaper mares that looked similar from the pics would be good for her... Pegasus.
I had to come back to say something after thinking about this. I hope you will not be offended. I'm just speaking in general as a female who has seen a number of couples wherein the woman became disenchanted with an outdoor sport or activity --- and not about you specifically as I don't even know you.
Anyway, what I'm beating around the bush to describe is that I would often see a couple getting into, say, downhill skiing. If it was the guy's idea (or he had already been doing it but alone), he would study up on gear and then get some really fantastic skis, boots, and clothing -- and then either give his wife his old stuff, or buy her some more "beginner" gear because after all she was not that "into it." Later (after she quit) I would wonder how it would have gone if she'd had "the good stuff." I'm sure in some cases it would not have made a difference; but in others it was probably a factor.
Again, I'm not saying this is you; for all I know you are getting a faded, garage-sale BC and she's getting the latest and best
(And too, she could get the Mares and hate it and then be sorry she spent so much.)