We've looked at and are considering the 3970. I've read extensively on the owner forums over there and it seems they just got done with a fairly major leak issue on their slides which was fixed, I think, on the 2016 models. Most of the other fairly major complaints involve the ducting of the AC and poor taping / construction of the air ducts resulting in poor air flow. In addition most of the unit is made with OSB so if it gets wet, there will be uneven and rapid expansion. So you must be cautious and inspect those seals, slides and roof. Same vein, there isn't a ton of support frame so much of the structure is held via vacuum bonded walls with relatively few studs. Other more minor complaints has to do with wires working loose and them using a **** ton of wire in a rats nest in the belly instead of using some kind of harness for each unit.
Overall for the price they seem like OK units just don't expect it to be trouble free. If you aren't afraid to pick up a screw driver and maybe some youtube videos you can fix a lot without help of the dealer.
We've owned a fair bit of rigs in our time and have found that they ALL have issues. I wasn't impressed with our DRV, I don't think there is an extra 60k in value over say a Grand Design. I think the mid end is a nice market where you get a large, well appointed unit but don't expect it to be trouble free, no RV will be.
2019 Grand Design Momentum 395
2018 Ram 3500 DRW 4.10
2014.5 DRV Atlanta (sold)
2008 Newmar 4330 (Modified) Sold