I use my recently acquired *istD L2 exclusively for M42 lenses, it's a relatively lightweight body, which helps when carrying a bagful of metal-and-glass lenses!
One of the attractions of using the older prime lenses is that they "force" you to consider the framing and composition, making you change position to get it right. A 6-megapixel file helps enforce this consideration, making it more desirable to "fill the frame" with subject matter, rather than zooming and cropping in the modern idiom
All of my "auto-only" lenses have had the aperture-pin either wedged or glued in the "activated" position.
Experience has demonstrated that an original Asahi Pentax PK-M42 adaptor is superior to the cheaper after-market alternatives, being manufactured to much tighter tolerances, making it far easier to remove and refit, if desired, without the need for tools.
One proviso - my M42 bellows couldn't be used on my cameras because the forward bulge of the prism/flash housing prevented the bellows from being fully rotated to screw them on. In this instance the bellows had one of the "flanged, non-infinity-focus" PK-M42 adaptors permanently fitted.
Enjoy