> Question is, are all thermo's the same quality?

I's say no (quality will vary batch to batch even in the
same manufacturing plant).

The OEM thermostat last about 70K. Many people who follow this
board (and know the typical issues) will recommend adding it to
the 70K service. On my 850 it went 75K and on my S70 it went
65K. I had two ready to go having purchased them in advance.
Takes under 30 minutes to replace. I went with OEM ($12 at
www.volvoparts.com) and will replace at the next 70K service.
Oh, both failed in the open position so the car ran cool (instead
of over-heating). Most reports indicate they fail open but some
have failed in the closed position. Most people notice the heater
not working as the first sign.