All the pumps are basically the same, However for your job you want Sanicon. That is the one designed to be MOUNTED..
I use Flo-Jet (Same motor, basically the same pump, there may be a difference in the macerator though (That is what most folks THINK is the impeller)
The Sanicon has a "Gray water bypass" it will slowly drain gray water without the pump running, this is the other reason for recommending for your install.
One more thing. On my flo-jet the bottom (non pump) end of the motor has a slotted shaft.. Make sure you can access this once installed.
If I do not use the pump for a while the blasted impeller sticks to it's housing (This is NOT the part you can see) and it will pop the fuse like a flashbulb.. A flat blade screwdriver and a quick twist of the wrist and it works perfectly.