No, you pretty much summed it up. Internal wastegates can work just fine, my buddy has a T3 with a .63 A/R exhaust housing with an internal WG and runs 12-15 psi daily and 18 psi at the track. Runs fine.

The advantage of an external is just as ^^ mentioned, it can controls boost creep a little better. If the opening on the internal is too small, the system will start creating more boost because the exhaust goes through the turbo, instead of out the WG. Typically, an external has a larger opening for exhaust to bypass the turbo, thus you don't get most boost that you want (say for example on a stock bottom end where you don't want more than x psi of boost).

They both work fine, but if you get an internal, you need to watch for boost creep, but as I said, people run internals with no problems all the time.

Brian

Red 97 Eclipse GS (420a) MTX
Custom Garrett T3 Turbo system
Megasquirt w/52 lb/hr injectors & a Walbro 255
Kicker/Alpine Audio (3 amps, 2 subs)
90 Cav 2.2 TBI auto (winter) <- yeah, it's fast