Wattbike Atom owner here....
I have had no issues with the Atom at all really. The convenience of having an all in one unit that fits comfortably at the side of my lounge is great. No faffing about with putting bikes on/off etc.
Not sure what the 'relevance' comment above means. If you're wanting some serious training workouts, then it's just as good any turbo, at the end of the day you're riding to power, s it does the same job. The ERG mode workouts in Zwift or on the Wattbike app are great, and really make you work for it.
The fact it doesn't have gears in the normal sense can take a bit of getting used to, but riding in Zwift etc, again I've had no issues and the resistance kicks in when you would expect it to.
If you have a decent desk fan reasonably close to you, you won't sweat as much as you might think, although I still have a towel and bits to mop up the excess!
I can't think of many cons really, aside from the price maybe, you have to think of it as buying another bike essentially. But the convenience of it was a really big factor for me. It takes up much less space than a normal bike/turbo setup (but it is quite heavy!)