I still have add-on TPMS I bought like 15 years ago for my motorhome at the time.
If you have metal tire stems - it works very well. In case you have leek, you will get warned.
Leaving the monitor on overnight will give you theft warning as well.
Since then the market was flooded (I paid small fortune to only manufacturer 15 years ago) so I would go with what local guys recommend.
Getting it local solves potential warranty claims faster.