I took a chance buying this frameset last autumn based on the very few reviews and other bits of information on the web. So now that I have ridden it numerous times, I want to share a short review in case anyone else wants info. My size L weighs 15.8#/7.2kg as pictured. Build is a mix of DA 9000 mechanical, Bora One 50 clinchers, Bontrager Serano Carbon saddle, and 4000S 23c tires. (And by the way, I am a 6'0" tall 180# ex-road and XC racer who was and still is a TT and sprint guy. I don't race, but I still train like I do and ride with a bunch of fast ex-racers.):
In short, this is really a super bike, and exactly what I was hoping it would be with few weaknesses. I was looking for what I personally believe is a true race bike: Stiff but stable (versus stiff and responsive). When I see a bike described as having "responsive handling" I think "twitchy at high speed". Today, most race bikes around my size (57.5-58 top tube, and just short of 400mm reach) have a steeper front end (73.5 degrees) and higher bottom bracket (67-70 drop). I wanted something lower and slacker like the three Merckx bikes I used to race a decade+ ago. At the same time, I also wanted a modern integrated aero bike. So I was trying to combine somewhat old school geometry with new school aero, which eliminated most bikes on paper. The Nitrogen Pro (which I was unable to test) rose to the top as having a little lower BB and slightly slacker front end. The few reviews I read said it was stable and reasonably smooth but still stiff. It seemed like a great all-around road race bike that happens to be aero.
Now that I own it, my own experience agrees. This bike is indeed very stable. It is not twitchy riding fast in a group or descending, but instead just feels very reassuring. It's stiff too, both laterally and vertically, and when I stand up to sprint, I feel less flex than any other bike I have ridden in my life. At the same time, it dampens road buzz surprisingly well and I never feel beaten up after a long ride. In fact, I like the bike so much that I am selling my Bianchi Infinito CV right now, which I had also purchased at the same time as a backup for days when I wanted more comfort. The Bianchi is very good too, but doesn't do anything better than the Nitrogen Pro. Braking with those proprietary v-brakes feels exactly as powerful as my other DA 9000 bike, and another bike with Ultegra 6800. It's actually amazing how similar the braking feels in every way. No worries about stopping at all.
The main weakness is tight tire clearance. The Conti 4000S 23c tires measure 25.1mm wide, and in the rear of the frame, that gives about 3 mm remaining clearance on the chainstays (sides of the tire) and the same on the seat tube (top of the tire). It fits, but you cannot cram anything much wider into that space. I am OK with that, though it would be nice to have a few more mm of flexibility.
Another weakness is annoying cable rattle in the frame. It amazes me how this finishing detail is overlooked by many engineers designing bikes. It's just not a good experience to hear incessant rattling every second of every ride. I have fiddled with the cables to fix it, and may need to surrender to the expertise of my local bike shop to fix it.
Anyway, that's my humble assessment of this excellent bike. Let me know if you have any questions.