I think they are quite a good idea.
I used to share a house in Cambridge & the only place to store a bike was in the house; there was no garage or shed.
The people I was sharing with were happy for me to leave it propped up in the lounge, but I always felt guilty about it because no matter how hard I tried to clean it after a ride, there’d always be a sprinkling of grit & dirt under the bike.
It also meant I would have to clean it before bringing it into the house & I also worried that someone would end up rubbing their clothes against the drivetrain by accident & get oil stains on them.
This would have been the perfect solution in that instance.
You can also get similar things that just go over the drivetrain, which seems like quite a good idea if you stuff your bike in the car frequently.