The biggest problem with aftermarket efi is keeping fuel in the lines and air out. Every in-tank pump out there has some method of keeping the pickup submerged - even if only for a a short period while you turn or stop. This sump will be uncovered at some point when you slow down or stop, even if the tank is close to full.
I have worked on a few mopar factory EFI fuel tanks where the "baffles" are really just a tin bowl welded to the bottom of the tank so the fuel pickup can sit inside it. Basically the same as the summit piece I linked, but with a step at the front so fuel cannot flow away during braking, and internal to the tank of course.
What would you do if you high pressure "external" pump failed in the middle of nowhere, you're still stuck !!
Fix it far cheaper, easier and faster than an in-tank pump. Many parts stores carry a generic in-line pump. I would consider an in-tank pump if it could be serviced without dropping the tank.
