Do you need the special tool to install the sleeve or can it be done without one. I tried to buy the tool but it is only available in a kit that costs $600.
I like to keep my equipment out of the weather, either in the garage or in the shed. If storage is a consideration the mmm has a smaller footprint and can be left on when operating other attachments.
If you are going to flush the system just top it off with water and check for leaks. If the level is low there is probably a leak somewhere that needs to be adddressed.