You make a good point, LCDR... but for $18, it seemed like a worthwhile thing to test.
The important point of the post is that there are EXTREMELY inexpensive TPMS systems out there (and therefore potentially suitable for some experimentation). If it doesn't work on his trailer, he can return it, use on a different vehicle, or - hell - eat the $18 and he's still ahead of the game.
There's still a wealth of low end possibilities to explore for someone who doesn't want to drop three figures for TPMS:
https://www.aliexpress.com/item/3256...d=7mI9tbU67Uc7
https://www.aliexpress.com/item/3256...d=NBfNIn2liSzX
etc
So long as it's being used for
supplemental monitoring (in addition to regular and attentive review of pressures and temps), I don't see anything inherently wrong with this route. It just doesn't give the maximum benefit that can be provided by a much more robust TPMS solution.