I got put off trying one on the road after a near-death encounter with a fixed gear gym bike!
It had a huge metal flywheel which must have weighed 20+ kg. It gave the bike a great feel when pedalling. I had intended to just warm up on the machine but it felt so good that I did 20+ minutes and built up to a 20 second full-on sprint. "
Okay, enough of that, time to switch to the rowing machine..." thought I, and promptly stopped pedalling. It took me a couple of minutes to extract my head from the ceiling of the gym, and another couple of minutes to reattach my legs!