I've assembled probably 8-10 of them, had a regular customer or two who commuted on the cross/touring ones, and done service on maybe another 8-10.
My overall impression of them is pretty favorable with some caveats. They clearly come from the same factories as many other brands, with similar quality control and factory assembly. There was some kind of issue with a DOA stem on one I assembled, and they took care of it promptly, I believe by comping the customer the price of an equivalent part from us. Having encountered one out of the box defect issue on the above mentioned sample size doesn't distress me at all.
You probably know this, but their "list" prices are a total gimmick. Basically those numbers are the highest full retail price anyone would ever pay for a similarly equipped name brand bike plus a 10-20% padding, and without regard to the value or cost of the assembly. Meanwhile, a very large number of bikes are actually bought from brick and mortar dealers at sale prices in the 10-20% off range, and sometimes more. So you can see that you do get some legitimate savings, but they inflate the number about as much as they probably think they can get away with.
You're also dealing with a bike in a box straight from the factory. They tell people to expect around 15-20 minutes to assemble it if you are "familiar with bicycle assembly," and that statement is optimistic to the point of being totally false. Their bikes don't present any special challenges or abnormalities, but as is usually the case, getting everything right simply is going to take much longer regardless of experience, and as with any new bike in a box will sometimes require relatively specialized tasks like hanger alignment, post/tab facing, and brake bleeding, along with the tools. The more routine assembly tasks of adjusting all the bearings, brakes, gears, truing the wheels, and fastener safety, along with all the tools involved for those things, are simply requisite. And, if there are any defects or quality control issues with anything, it's up to you to spot them and deal with them in a way that's safe and appropriate.
So in summary they're a legit way of getting more bike for less money, but it's not all upside.