One problem with BB dynamos is that they are tricky to mount. Whether a particular dynamo will end up fitting a particular bike is an issue of chance. Union sold different versions to facilitate the fit. Another problem is that they require tires with a continuous thread along the center. The final problem is of potential slipping in the rain. I rode with a Soubitez BB dynamo and it was actually very good not only in the rain but also in snow. However, some people complained that the Sanyo was not that good with that respect. I actually happen to have a couple of them in storage but never mounted one.