Folks, if you've recently upgraded or renewed your annual club membership but it's still not active, please reach out to the BOD or a moderator. The PayPal system has a slight bug which it doesn't allow it to activate the account on it's own.
I have never used the prefilter box so can't comment on that.
The reason it is only listed for those 3 pumps is because they are the ones that are recommended for that skimmer. Actually the Rio 1400( which they quit using) and MJ 1200 are for the Remora and the Mag 3 is the Remora Pro. The MJ 1200 and 900 are the same housing with a different impeller so it should work with the 900 also, of course the performance of the skimmer may be compromised by using a smaller pump.