I have 3 M42 Pentax lenses but I sold my Spotmatic. Didn't really like it for some reason.
For me, the biggest reason to not like a Spotmatic was stopped-down metering. Of course, your reason(s) may be different.
One way to avoid the annoyance of stop-down metering would be to avoid metering altogether, as some have suggested. ;-)
But if you want keep the meter without having to stop down every time you use it, then keep in mind, not every M42 lens will allow you to meter wide open. And a lens that allows open metering on one M42 camera may not work the same way on some other M42 camera.
For example, the Pentax Spotmatic F does allow wide open metereing, but only when paired with Super-Multi-Coated (S-M-C) Takumar lenses that feature an aperture coupling tab. (I believe Pentax added the aperture coupling tab in the early 1970?) So if open aperture metering is important to you, the first thing to check is, do your three M42 Pentax lenses have the aperture coupling tab?
If your Pentax lenses are new enough to have the aperture coupling tab, then they should allow open aperture metering on a Spotmatic F. But if you are looking at other brands of cameras, do some research before assuming your Pentax lenses will provide open metering with a given brand and model. Sometimes other brands used different bits and pieces on their lenses to make open aperture metering work.