My personally preference for for 12 gram changers are rat attack bucket changers.
Carter makes these, Taso made some and the originals were actually made by some buys in Texas (who I think played on the boonie rats).
CCI bucket changers are usually 10-15 dollars cheaper and also work well. Drop outs are another options but I don't prefer these because they take a little longer to change 12 grams in and are longer overall.
I don't recommend the cheapo aci/brass eagle bucket changers but they are cheap and do work. They usually require more turns to get a cartidge in or out.