I had been eyeing it for a while and finally got it.
It has a very beautiful and detailed construction that will keep you occupied for quite a while (a full 3-hour session if you're not in a hurry).
The instructions are very detailed, but you need to pay attention and not skip any steps.
From what I've seen, it also has several mods and alternative builds that you can play with. The batteries are easily accessible and you don't need to remove more than 2-3 pieces to change them. It takes 6 AA batteries, but it would be preferable to have a rechargeable battery pack.
I haven't had a chance to play with the app and see it in motion yet. I will come back with an update + photos.

Update: After a few trips to the mountains and meadows (parks and 1-2 small forests), I have to say that it is very close to what I expected.
I set up some trails (10-15m) with obstacles like rocks, branches, etc. and it was a lot of fun to take it for a ride. It easily climbs sideways obstacles of about 7-8cm in height.
The speed could be higher, but it would lose in torque. With the 2500mAh batteries I currently use, you can play for a good amount of time before it starts showing signs of fatigue.
The app is user-friendly and easy to understand. It also has some interesting challenges. There is a slight latency in the commands from the mobile phone (tenths of a second, but noticeable), which is not bothersome as long as the set doesn't reach high speeds. I have made some small mods to it that gave it a few extra millimeters in height. Overall, very satisfied