What's not to love about The Zipster? It's a superbly simple concept, well executed, and it results in a well made, climb-into, wraparound belt with no annoying clasps or fasteners to fiddle with, just zips to secure the front and back pockets. There are also two large flap-closure pockets either side for whatever you need to carry that will fit.
While I'd read before buying that larger smart-phones will fit into Hipster/Zipster pockets, size is relative and the current incarnation of The Zipster might not be right for those with smart-phones at the bigger end of the scale. My phone (OnePlus 6T) in a branded 'bumper' takes effort to squeeze into either of the zipped pockets. Without the case, the phone can slip into a zipped pocket by scraping the phone against the teeth of the zips. However, this is not the sort of thing you want to try with sweaty hands during a run, and definitely not something you want to try with sweaty hands AND a slippery glass-bodied phone that's not in a case.
The phone will however fit into the really handy, easy access and larger flap-closure pockets that feature on both sides of the belt. I've used this now for dozens of runs and there's never been any hint that the phone might fall out.
If I were going to design the perfect Zipster-style belt, the zipped pockets would be ~10-20mm taller and wider. I wouldn't mind a dedicated fastenable key pocket large enough to take a few keys and keep them separate from cards/phones, etc.
If anyone at Nathan is reading this and looking for pre-launch testers of newer versions of The Zipster, or even the ideal Zipster as described above, do please get in touch! :)