My parents spend the winters in La Quinta, CA (near Palm Springs) and almost every restaurant (and many residents) out there has them -- even though it might be in the 80s during the day, the Desert nights are very cool.
I would say that they heat
close to a 10-foot radius, maybe slightly less -- but if you're too close, it can get too hot as they do generate a lot of heat. But without them, nobody in the desert would eat breakfast or dinner outside. I'm always surprised how few restaurants here use them because by using them, many restaurants could extend their outdoor dining seasons into October.
Although I don't know where restaurants store them, I suppose multiple chains and locks might work, as I've seen lots of restaurants do that with tables and chairs, and I know the heaters are heavy.