I hadn't actually decided on which one I was going to use yet. I bought a selection of different ones off of eBay a while back to use on various projects. So far one has ended up on an old XL250S I built for a friend, and it looks good on there. I really feel like it's hard to go wrong, though of course the purists will object. If you can live with that, then the world is your clam. Just searching eBay for "bobber tail light" will get you thousands of results
YES! These are all cheap cinese tat! But they are lightweight and inexpensive, so less likely to make your fender crack and easy to replace if they fall off.
I have also considered making a tail light out of an old MAG light--it can be done, but it's a little complicated. Mine is about 90% done, I have no idea what I'm going to put it on--it was more a case of "I wonder if I could make this dead MAG light into a tail light...."