we just got a little tour of the targa's at a shop from a guy that uses / loves em. like you mentioned, he said they are adjustable in tons of ways. other features he mentioned where the flat base for your foot to rest on, but i think the 390's have that also.
the feature he liked the best was this adjustable tension piece on the ankle strap that basically held the ankle strap away from the foot pad. so when the ankle strap is popped loose, if you set the tension piece really tight, it will flop all the way open and stay there. seems nice if your are in and out of that binding alot, to not have to organize your straps every time.