Since there aren't many reviews here, I'll write one, but please note that my experience with these boots at this point are limited. I'll retract my review when more people start to write in. (Experience so far: two resort days). I'm an ex-alpine ski racer, started to tele ~15yrs ago. This is relevant because I'm used to stiff alpine boots. These boots are buttery compared to alpine race boots, so I was a skeptic when I heard how "stiff" they were. I still concur there; they're not as "extreme" in the stiffness range as people will have you believe. Also, in the store (BD in SLC) I tried the Customs & the Pushes on back and forth a bunch of times and didn't see a ton of flex difference (note: hard to really tell without being locked into a tele binding, and boots were at room temperature).
Existing setup: old T1's (like 3rd gen), G3 bindings, tried multiple pairs of skis.
Skiing: What I did notice right away was that this boot is far more laterally stiff than my old boot. That apparently makes a huge difference, as I was in far more control over the ski edge than I ever have been on teles before. It felt awesome to be able to carve so easily, where it was such a difficult rarity with my old setup.
The bad-news/good-news for me: getting these boots was like mixing single malt with Sunny D, or putting catchup on a prime fillet. They make you quickly realize that you need a much stiffer binding (like the BD 01 or the Hammerhead) to get the benefit out of them. With my G3's, I can lift the heel maybe 2" before I notice the binding providing any resistance. So reader beware, these expensive boots will make you want (or you could say, they require) new bindings and of course some new stiff skis to really reap their benefit.
I'm in line to follow through with the above plan, so when I do (and when I have enough on/off-piste days under my belt), I'll let you know more.