The mouthpiece on mine, is a pretty solid connection. While the piece doesn't need keck clips, if available, I would certainly use them. The mouthpiece is a tempting spot to grab. Though, even with the clip... I just broke myself of the urge to grab it there. Its small and light enough, to grab anywhere.
As for the RezBlock, I didn't change my water that much, unless I was traveling back in the day. We used to think it was a good idea, to strain and scrape that nasty black tar when herb was scarce. 3 days was nothing back then. 3 days now? I'd puke. Except for... RezBlock. It doesn't let the residual stick or clump. It breaks it down, that's why it looks so murky in the video.
As for removing other stuff, such as actives in your herb? No. I haven't noticed any change in my medications, nor amount I have to use. If you're referring to things like hard water deposits, I'm not sure on that. I use only distilled water. HOWEVER, once you have given the piece a full clean-out, including removing hard-water deposits (couple nights soaking in Simple Green, should take care of that)... I believe the RezBlock, will indeed block that stuff. It just doesn't let things stick to the glass.
I probably won't keep water/RezBlock in my pieces for more than 2 or 3 days. I mostly likely it, because its reopened my entire glass collection. Not having to worry about ISO washes, when all it requires now, is a warm/hot water rinse... makes using hard to clean pieces, enjoyable once again.