Ive been using it for quite some time afking for hours smelting it and its kinda good i have more than a chest full of blocks and like in the early game lugging around a stack of blocks not only as a great fuel source being like 3 times better than a stack of coal but a decent food source too giving 9 whole stacks or dried kelp the blocks can also be traded to butchers and might give some exp after smelting for hours but im not sure if it gives much xp but kelp is nice to have because you can just afk using fuel to get more fuel and using a conduit or nautilus you can farm it kinda easily