Sorry for the delay with a followup. Wheels arrived and I installed them, and due to unusually cool weather here I've only had to mow once.
Overall quality seems to be pretty good. The only thing I'm not fond of is that there's no through-bushing, so you can't actually torque the axle bolt. You have to sneak up on the torque, to lightly load the outside spacer bushings against the inner race of the bearings. If you don't do that, the spacer bushings spin on the axle bolt which will wear the bolt. If you over torque, it will wear out the actual bearings.
But as I said, the overall quality seems better than the junk that came on the Bush Hog brand finish mower, and the price was certainly better. Time and use will tell on how durable they are.
Thanks for the tip on the source!