Nice monk item plus you get a charisma bonus, not that monks need it, but sure can't hurt when selling to vendors. My guess is it gives almost same benefit as Dragonbone in combat (for monks that is), I'm sure for Bards its a whole different story. Not sure about higher levels but the 0.4 difference in weight between Seahorse and Dragonbone could actually cost me about 2AC if I'm over my weight limit at level 30 (only takes a few coins). So, with that in mind, you still have about 2 more AC than Dragonbone but 2 less on strength and agilty stats. Probably an even trade off in terms of combat situations. Dragonbone and Seahorse Spine both sell for about 2500pp on Lanys T'Vyl... seems fair enough.
Hmmm, looks like something I'd like to get for my selling/buying gear. Being a dwarf warrior with a low charisma, even amiable and warmly shaft me at the merchants.
Pretty monkable? Hell, with Ac 8, +5 Str and only 0.5 weight it's one of the best bracers a monk could get! I'd be willing to drop a fair chunk of change on one.