i have had several of these tanks.
advantage is connect fuel lines to outside, install, and you are ready to go.
never had had problems with tanks getting air in them or problems with engine performance.
have used them for nitro, gas engines.
i have even used two of these tanks in a 30% scale cap for the smoke oil.
cannot remove fuel from tanks unless you remove thru line that goes to carb
if you place your airplane to be standing on its spinner, and then lean top of plane back.
that's how i do it, and i draw fuel out thru vent line.
2nd disadvatage is cost.