I'm not a fan of the idea of pups that can stop working should a battery be dying or dead. I'd prefer an active circuit after the pups that still allows for passive use when needed or preferred.
That said, Gregory Kochory uses them in his guitars and they sound stellar. To be fair, however, one must acknowledge that there is not a clip of Greg playing a guitar that didn't sound great (allowing for the varying recording quality and audio compression to keep files to manageable size)...and that's all Greg, not the myriad gear he's played through.