I would recommend Test strips... ... to wipe your bum with- but only if you have a very small bum... otherwise- I'd even prefer the liquid kit for that purpose too! Ahhhh... the joys of a GH test bidet!
I started out with the strips... I didn't find mine to be unreliable- in the sense that they kept giving me the same results- and when I finally found a liquid kit- it gave the same result.
However, the test strips are horrible to have to read. I suspect a lot of their "unreliability" is the difficulty it is to read them in comparison to a liquid kit... the colours almost never match what's on the comparison chart- there is massive amounts of room for human error, it's usually a case of
"is this this green-or that green... it really doesn't look like either?"
I think I usually asked my wife and my son to confirm each strip because I could never detemine "which greeny bluey yellow is this?"
Liquid kits cost more to start with but you get so many more uses out of them they end up being cheaper in the long run.