I did another replacement yesterday with some Shimano BO5S-RX pads; the RX indicates that they're resin. I bought them from Amazon, which I regret, as even though they came in what looks like genuine Shimano packaging, I've become increasingly leery about counterfeit products from Amazon. That said, I don't understand why the previous pads started to squeal so badly -- it's not clear to me that it had anything to do with their inherent quality.

In any event, I'll be curious to see if how these hold up. If they start squealing within a few months again, I'm going to suck it up, take the bike to my favorite LBS, and see what they recommend.

Thus far, I'd say that I'm a fan of the belt drive and Enviolio CVT hub on this bike, but for my riding and braking needs, I'm wishing it had old-school cantilevered rim brakes -- the hassle that I associate with the hydraulic disc brakes has significantly exceeded the small benefit that they provide, IMHO.