I have one. I think it does N-P-K and Ph. I've only used it a time or two not sure why, maybe the variable of use? Soil moisture, how deep to insert, measure contact, the black magic inside the case, lack of confidence of a do all tool? Probably a matter of trying it and not understanding the results or getting mixed results or something ... Could have very well been user malfunction, I'm that way sometimes. They very well could be an effective tool.
I do use and have had what I think is good success with something like this. I like it because it's an actual test and a uses basic scientific process and it has defined controls. Kind of fun to do too.
I don't really have grass so I can't comment specific to Ph and grass.
I should do a comparison with the stick next time I use the kit.
https://www.harrisseeds.com/product...st-Kit-small?gclid=CKqqlOT6-dMCFUpNfgodKyEDRg