I put a 2" Sunpro mech temp gauge from Pep Boys, and shortly afterward the needle started binding up and sticking - I'd have to tap the gauge to free it. After some argument with the counter guy at PB (he insisted that I must have damaged the tube to the sender somehow, although there was no visible damage), I was given another one that has worked just fine for some years in a daily driver and seems quite accurate.

I'd suggest you test any mech gauge before you go through the trouble to install it.