Good – they just work. Had mine a year and done nothing with them and I commute year round off road. They seem happy to go where you want them to go. They often don’t seem to be there, in that the bikes rides the same with them or my rigid Pace forks, it’s just a lot more comfortable.
Bad – they are heavy. At 60kg even with the softest spring and no spacers I can only get 50-60mm travel out of my 85’s riding cross country.
I’d say they were ideal for a single speed if one of your criteria for riding a single speed is low maintenance and if you want a fork that makes riding what you ride on a rigid more comfortable without changing the overall feel too much.