There really isnt a downside to a tang sight attached to the wood, some real vintage target rifles had just so done. The oft repeated 'wood changes with humidity' effects on a wood mounted tang sight has never actually been documented as far as I know......At a shoot we all sight in anyway and just the light conditions cause more trouble day to day that that sight will (unless you are in that rarefied air of the true long range competitors).
At that price, if c/w the tang sight its likely a good buy; even though it isnt going to be an expensive tang sight, it could work out well.