Used Triple S before a few times as well as cheaper options. Cheaper options weren’t as good (orange peel, powder in threads etc) – Triple S were excellent but more expensive (think it was about £100 for a full sus frame but thats going back 10 years or so). They do classic motorbikes etc mostly so are well versed with masking off the stuff that should be masked off but any frame I’ve had powdercoated, regardless of who did it, required a certain amount of prep before building back up.
That said, I’ve heard good things about LSN in the car world and getting wheels powdercoated etc so if I ever needed a frame doing again I’d take a closer look at them as they’re closer to me now than Triple S.