...or is the park tool the only one that really works?
Ehh? Just wondering about the phrasing. Park tool may have earned a good reputation with some of their tools, but in spoke tension meters, theirs is not really the gold-standard be-all end-all kind of thing (if anything, it's more on the lower end of the spectrum, kinda pricey for what it is, tbh, but park tool).
If you're talking about round spokes in large wheels, almost any type could give you somewhat repeatable readings. With thin bladed spokes or small wheels (little space between crossings or spoke ends), things get a little more complicated. Also, tension meters may need a little practice and a steady hand.
Personally, I only use thin bladed spokes and prefer the Brandt design (I have an older Wheel Fanatyk, but there are also those from that Polish guy) over the pliers style ones.