I've never bought one, or even looked at them seriously, because I'd rather suck it up and ride outside, even if the weather is a bit shit. However, I've broken my ankle and done some ligament damage in the process, and am looking at a couple of months of being able to bear weight, but not yet being back to full activity, so it seems like it might be time for one. What's good? What should I be looking for? I don't know much of anything about them.