I have one- we found an used spin bike from a gym. I made sure that I could put real bike pedals and seat on it. Otherwise it would be horribly uncomfortable.
I don't like not having a freewheel. I keep forgetting it's fixed and attempt to stop pedalling to stretch. I hate indoor riding so I don't use it often.
good points: it's easily adjusted so my wife can use it. It doesn't need maintenance and I don't care if it gets all sweaty.
bad points (vs bike on a trainer): No freewheel. Wrong bars (I need to machine a fitting to get regular bars on it).