The trouble with Mega Key adapters is that there are a large amount of adapters floating around that call themselves "Mega Key" adapters, and not all of them do work with lockout carts. I have been stung by that one before :/
In my opinion, the Nitro 2 is a safe bet, because as far as I know there aren't any dodgy knock-offs of it that also call themselves "Nitro 2". If you get a Nitro 2 then you know you've got the real deal ...
Vroomfunkel
P.S. In answer to previous question .. watch my auctions