I have a Timberline 850 and its build quality is fantastic, it's also the heaviest grill I've ever assembled!
I have been critical of the WiFire performance from day one of owning mine, delayed or missing alerts to my phone made it useless. Traeger has been slow to correct this but they have finally reworked the architecture of how the grill communicates with your phone and it's much better now. The recent complaints about WiFire is the poor roll out of the update, it broke the communications between the app and grill and in some cases, grill to network (thereby preventing recovery). Many of us managed to get updated and are back up and running while others are stuck at various stages in the process. This will settle down fairly soon I think.
The grill performance for cooking has been stellar, I have cooked in very windy and cold (not freezing) conditions and the double insulated Timberline with gasket sealed lid has worked perfectly, recovers temps very fast after opening the lid. The super robust stainless grids are holding up great. The shelves are made well but are poorly designed, I'd much prefer a larger, folding front shelf as the stock one is pretty much a joke. I really like the Timberline's sleeker design with internal grease trap, never liked the outside bucket that my previous grill had. Also the internal convective swirling of the smoke, and super smoke settings are nice refinements to these newer models. The cover is expensive (as is the grill) but so far my grill still looks like new after six months outside.
I'm currently a very happy user.