oh wow great to know! i am running a 406 on my 75g tank also! we are very alikeEasy, only inconvenience I guess is it's pretty large and heavy so it's hard to pull out of the tough spot where I put my unit
Also when disconnecting the hoses i always get a small spill from the tip of the hoses. No big deal, the unit is on a rubbermaid so it doesnt matter. But i havent experienced the same with other canisters
The auto priming works great,
I have a 406 right now and will replace it for a second fx6