Thanks for the response. I have access to tire changing and balancing equipment so for me its not the same struggle. I'll agree this puts me into a bit of a different situation.
Removing the current valve stem thread on sensors to check the air pressure is a bit more work than just the caps. I am using the jam nuts that came with the sensors and while not impossible, it's a chore that I don't have to do with the tow vehicle (having internal sensors) when I check it each time. Also, removing and putting external sensors back on does change the pressure more than just a quick check using a pressure gage. How much more, probably 3x ish. How much is that, maybe 1/2 psi or so. Just guessing by removing and replacing them 4 or 5 times in a row and monitoring pressure with a gage each time I can take a reading.
I am however concerned with valve stem life. I have recently had a low tire found before a trip and discovered it to be caused by the seat of the valve stem to the rim. I checked all the rims with soapy water and found a second with a very slow leak in the same place. Was the centrifugal weight of the sensor flexing the stem more than it's intended rating causing this? I don't know but I wonder if the valve stems were designed to have this extra weight put on them. I doubt it. Am I considering updating my stems if I stay with the externals? Yes, but I will need access to the inside of the tire then as well.
Also, the update times for psi readings on the Tymate can be slow, even with the installed repeater. I have observed the update times of my stock Schrader 29015 units on my tow vehicle to be noticably better. Anyone reading about trailer tire blowouts has surely come across complaints where users felt that that installed tpms sensors didn't warn them in time. Maybe just posturing on their part, maybe not.
Do I think the screw on sensors are a major issue? No. They seem to be used quite often with high success. Including mine so far! And before all the digging on my end, for me externals were better than nothing.
Again, for me having access to the needed equipment changes how I can approach the situation vs another.
YMMV, I'm no expert, use at your own risk, don't run with scissors, don't pet strange dogs, etc. and other standard disclaimers.