Here's my story and I'm sticking to it:
1. 0.72 mag. viewfinder & 28mm lens: The whole viewfinder is a 28mm field of view. The 28mm framelines aren't required. I have two otherwise indentical bodies, one with & one without the 28mm framelines. I use the 28mm M-Hexanon lens on either body. No worries.
2. Uncapped lenses can cause burn holes in cloth shutters.
3. Given a choice between bodies with recent CLAs and bodies without, go for the one with the recent CLA. Said another way: Figure $300 into the price of a body for a CLA.
4. Pentax Spotmatic Metering: The best combination of meter and shutter and ergonomics and build quality, hence the best camera from a shooting standpoint, in the M line belong to the M5. The only function in the body that requires a battery is the meter.
5. LTM lenses can be used on M bodies. Not sure if that was covered above.