Shake light : interesting to teach a few physic/electricity facts to kids.
As others have said, the output is rather feeble, but you can find uses for such a light. + new models are more powerful.
Caution : strong magnetic fields....

Crank light : I have one in my 72h (or more) kit, along with battery LED lights and spare lithium batteries. I don't use it, it stays in the kit. IIRC the output level was not very bright, but much brighter than the shake light. + the run time was much better too.
OTOH, I use a crank powered radio every day (that's my daily physical exercise... <img src="/images/graemlins/grin.gif" alt="" />). 30 sec cranking gives about 20-30 minutes radio (not too loud), depending on the time of day/weather as it also includes a small solar panel.
Seems to work fine ; nothing broken up to now.