...that this product will work well with any old 'old' router, their low-speed broadband, or their bargain-basement data plan then they're placing 'hope' above 'reality'!
We had issues initially setting up just one device - everything else on our network and broadband worked fine and had the latest updates applied, but it took a new router PLUS its latest update BEFORE we could get a connection. Even then, the first thing the device did was update itself! Once one device was set up though, the other one went through the process smoothly.
IF people have problems with these devices then it really is back to basics: NO assumptions, trust NOTHING in your existing installation, DO NOT TINKER with configurations in the hope that you'll get it right! If it works, it works easily because everything is correct already: standard configurations FIRST, tinkering later!
One other key point: PATIENCE is a virtue - the warnings in the setup process that "this may take several minutes" are quite correct, so when you get to those points, go and make yourself a cup of tea!