It's absolutely fine. I bought a set of 15's a couple years ago and they're excellent. Powder coating is so thick you can barely see the "trailer use only" stamping- you have to know where to look.
As far as safety is concerned I feel more confident with them than my original 16's that are usable but you know how it is after 67 years...minor dings here and there, maybe a smidge of runout, not to mention I'm running them without tubes and they're riveted. I also think they're harder to balance.
There's no rivets in the modern wheels and they also have the bead retainer ridge and undoubtedly made to a tighter spec than wheels from almost 70 years ago and don't need the massive balance weights my 16's always seem to need. I say from my own experience--buy with confidence.
