i bought one thinking (like you napper) that when its gone stiff arun down with a cornertrowel just fills the corner nice and the adjustable trowel will eliminate that trowel mark a normal one leaves behind..
not a bit of it mate, its only adjustable from about 100 degrees upwards, its minimum angle is over 90 degrees, theyre made of a really soft plastic (almost like rubber) so they bend like f''ck...
and as for 135 externals, i just do em freehand anyway...
wouldnt recommend it...