I see these kits all over the place; are they any good? The sort of things, using either some sort of a spoke or even a hub attached to the wheel; that promise to charge your electronic devices. I'm getting into cycling, and one of my 'thoughts' going into this is that I'd really like the ability to keep my phone charged. Especially if I want to use my phone as a bike computer. There's a lot of inexpensive generator-chargers. Wonder if any of them work?

My other thought, was to mount a USB-chargeable battery in line with the generator. I.E., one of those smaller battery paks, that can charge from a USB source (as opposed to a 110V source), attached to one of these generators. And then the external battery, attached to my iPhone. My thought process is, the external battery pak becomes a buffer. And prevents the issue of potentially charging starting and stopping as I start and stop (or even slow down to a point potentially too slow for the generator to work).

Thoughts? Are those junk and a total waste? Or are there usable (and inexpensive) ones out there? If they are particularly expensive; then a dedicated bike computer seems like a better investment. But if there are good cheap ones, then the ability to charge my phone on the bike seems more versatile than just not using my phone and having a dedicated bike computer.