Hi
Did the 305 have taps to turn the flow to and from the tank off? If not, the Eheims with the full tap connection kit will save you from the flooding issue and are very efficient and reliable
They have two pairs of taps fitted inline on the pipework and you just turn them off when doing maintenance so you can remove the cnister with no leakage and no reprimimg.
The 2217 would do a grand job on a 55, just make sure you get the "plus" kit - all the media, pipes, taps and spray bar included.
If you really want to go with an internal, hopefully someone will be along who knows about the good ones soon