Since The Source is basically the same RSII, I can tell a little.
RSII is a good pickup, at all, although it is difficult to find the right spot, and more difficult to keep it sounding good. If the weather changes drastically, be sure you'll have to spend at least 10 minutes to find the right spot again.
It sounds very natural and the arco sound couldn't be better. Feedback happens, yeah, but any pre with phase inversion can handle this.
If you run it through any DI (even a passive one) it will remove the piezo quack and will sound like a microphone, really.
So I'm not surprised that people are getting good results with The Source. As I don't like any permanent install I wouldn't go for this new one, and although RSII is not very easy to remove and install on other basses, it is possible and it can be useful when travelling, renting basses, etc.