Sure, it looks kinda clunky and doesn't have Zeiss glass, but the results I've seen speak for themselves. It's a system. Apart from lacking a few things like motor winders, this is a complete system - there's a full range of lenses and accesories available for this camera. It's widely used. This is not an obscure camera, and it's possible to buy lenses and bodies on the used market at reasonable prices.
People are pretty familiar with it.
As sold straight out of the box, the Pentax's MLU uses the battery - the MLU is fired and held by solenoids, meaning that it uses battery current whenever MLU is on. This is OK for some studio work, but quite unnaceptable for things like flash fill outdoors. This has never bothered me, but it's quite a limitation for certain types of photography. No removable back. Neither of these is ideal, but the lack of a removable back turned out to be less of a limitation than I'd suspected.