Perhaps a bit of a novelty given the rechargeable battery argument others have mentioned. I imagine distributing a bunch of these with batteries and having a central dynamo-powered recharging station that gets shared throughout a community would be even more practical.<p>The first thing that came to mind when I saw that it lasts 20 minutes would be to use it as a pomodoro timer. Code for 20 minutes, then be forced to take a break, stand up, lift the weight, etc. You get a micro-workout as a small bonus. Again, it's a novelty but sort of a cool one at that.