Well, the ring of burning, ring of coldfire, ring of scribes, and ring of wayfinding are all fairly reasonably powered. The other three are somewhat stronger though.Overall this is incredibly powerful, and should not be used unless they are some sort of plot-related set of artifacts and the BBEG is activly searching for them. (and slowly gaining them, making him more and more dangerous...)
I did kind of see them as plot-related items, or as items with a history and a unique feel that could be used for fun stuff.
Well, I dunno, scribes and wayfinding seem alright to me. Burning too (wooo, fire damage). I could see a party with those three.PCs should NEVER get hold of more then one of these.