Originally posted by jonhock To the best of 'my' knowledge they are the only 2 pentax flash units that have a sensor built in that enables the units to "read" the lighting and accordingly adjust the amount of light they put out.
+ the handle mount Pentax AF400T.
And of course the current 540 and 360 (I know they may be out of the scope of this thread).
Back to the OP...
Why limit yourself to Pentax flash units? I'm using many old flashes. Except for 2 copies of the current 540, all of my flash units are non-Pentax.
I recommend: Nikon SB 24/25/26/28; Sunpak 30DX, 36DX, 422D, 433D, 444D, 383 Super (or its clone Quantaray 383); Vivitar 3700, 5200, 5600. If you don't mind handle mount flashes, add Metz 45CL-4, Sunpak 555, Sunpak 622.
All of these have safe voltage, and have light sensor for auto mode, and can bounce & swivel.