I have had really good results with my "extra" sensors, have always run 3. Most of the time the other two are somewhere in the house, or pool during summer (probe type). But when I put them all outside or in a room, they track pretty good to each other.
I got the 123 version from the dog for xmas (the extreme cold version) Afraid to install, my stock shack/nextech units have never had trouble with the cold, and i have been tracking at 99-100% for temp lately on madis, so I will leave it in the supply drawer till needed.
very small screwdriver? I have not looked at the new unit outside the box yet, but the "extra" sensors have always had 4 screws, but they are just the normal small size phillips (I believe its a #1). Not like a glass repair kit size or anything.
Andrew
OK! I have the THGR122NX up and running and have it substituted for the THGR968. Compared to known stations, it is extremely on the money. I am a 95% happy camper. 
I will say that the range is not quite what I expected. The batteries (which were supposed to be included, but weren't) may be weak. When it gets a little more pleasant outside, I need to find a better placement for it. With the clouds and rain, I don't think solar heating is going to be a problem for a few days.
Oh, one more thing. You need a very small screwdriver to open the battery compartment.
From the FWIW Department.
