I've got a concept 2 rower, got it not long before the COVID scam, I could have sold it during said scam for a fortune as they went through the roof!
If you get one they're all pretty much the same as it's based on a big RSJ let's be honest
but just ensure you get a PM3 monitor or above, you can link these to PCs and stuff (if you cba)
Obviously budget for floor space, I use mine for half a year as I like to cycle in the summer. (You can split it in half and it takes up a lot less space vertically)
Maintenance on the concepts are cleaning the rollers under the seat and oiling the chain (takes months to be required) It's an RSJ and they're built to last to the extreme, we have the same handle from when it was made in the late 90s I think, it's made of wood and the more modern ones are plastic, it's been in a gym and a school prior to me having it, it's not breaking any time soon!