I've only used ATI but have had great luck with them. I won't say it is the best as I know Triton bases their platform on theirs. I will second what
@JimWelsh and a few others noted in this thread and others that the one you noted isn't the greatest.
Again, I've only used ATI but here is what I like about them:
1. Bonus RODI check (not sure how accurate but it is there for you to reference)
2. Great support - I've sent a question in and had a great response and dialog
3. Seem to match my manual test results to include my Trident
4. Caught two issues
a. Low salinity - folks here in this forum asked if I used a reference fluid as part of my checks and post calibration, I said no, picked some up, and the numbers matched ATI's. I was in error
b. Low iodine - ATI reported twice it was low and then I dosed and the next result showed it cleared. I'm guessing their process worked.
In any case it is a bit more at 44 bucks but I like it. I send 2 or 3 off a year and use it as a reference to my tests and the tridents plus the overall water chemistry. Seems to work as long as I use it as a reference. But it did catch a couple of things for me and they are right.