So, I have one. The longest one. I've not had it long but it's pretty spectacular (of course, might just be new bike syndrome ).
I'm 6'5. Most XLs aren't big enough. My previous bike was an XL Yeti SB95C (amazing bike). To get seated reach with short-ish stem, I had the saddle pushed all the way back on the rails. All my previous bike had been this way, so I was used to it. But still, seated steep climbs meant riding the nose of the saddle to avoid the front lifting. And when descending, the top tube, though fairly long, was still not long enough.
Now the trend is for longer top tubes, but still, there is only really one production bike long enough - the Mondraker. And then, along comes the Geometron and it looks great. The big difference in the reach between it and other long bikes (Mondraker, Strive Race, Kona Process, Transition) is the steepness of the seat tube means that the length is forward-biased.
My geometron climbs amazingly. I expected the front to wander and flop a bit, but it's pretty easy to stop it from doing that. It pedals really well (and not just for a long travel bike, for any bike). The frame is bombproof and the suspension bearings are huge and stiff. Out of the saddle sprinting is impressive.
Going down, on my limited time with it, and my limited diagnostic skills, it's very, very impressive. Super stable, as you'd expect - get your weight over the front (not difficult when you are my size) and it corners brilliantly. I have 800 wide bars and a 35mm stem. It'll take a while to get used to the extra width when I'm in the trees. Going off drops, the bike doesn't even blink.
In the end, the chainstays are at 445 which isn't *that* long (same as my Yeti).
It's a DH bike which pedals (very well). It's heavy but I don't think that matters (my weight is far greater). The suspension is top notch, having been given the Mojo treatment. I have mine set up for steep trails, but it seems pretty good on the flatter, pedally stuff too.
Biggest drawback - it's too long for my workstand! (Feedback Sprint) unless I clamp it at the rear wheel (painful). It only just fits on my roof rack.
In the end, I bought mine because it promised to fit me, be bombproof, and offer something (fairly) different to your standard trail weapon. I can always lower the travel if I need it steeper (and shorter). But I suspect I won't.