Okay in a dry, warm place I guess but in the wet and grit of the UK? I doubt it. Anyway why meachanical when solar is the way forward - I'd be interested in anything that charged my phone on multi-day trips. We tried a cheapo Chinese solar charger on C2C but it was garbage and didn't even work at home in the garden.
The GPS-powered direction thingy above looks as if it would sell well in Lakeland, which is a shop full of solutions looking for a problem.
Buy a Shimano hub dynamo. Either ready built into a wheel or to build in yourself. They can be had from as little as £25 from ebay or the likes of Rose bikes. I bought a ready built one with a basic but functional rim for under £40
Front headlights are also available with usb charging capability, or something like a Biologic module. Weather proof and reliable. Perfect for commuting and touring.