Lamotte have the bets hobby grade track record, they are borderline research monitoring grade.
Still, even the best test kits and methods need to be calibrated.
LeftC has a simple easy to understand way to do that, search here on TPT and it'll pop up.
Cheap test kits, you get what you pay for.
If you plan on doing routine regular testing, it really pays and makes your life much easier to spend a few more $.
I was ever really able to convince folks of this, mostly because no one ever bothered to use references for calibrations.........so I figured I'd argue for EI dosing.......
You can still test and modify your EI type dosing.
This is essentially what I suggested in mid 1990's.
A step up from Lamotte are the Hanna colorimeters which are pretty nice, but going from 50$ to 175$ starts to be quite a hit for most.
For PO4/NO3, I'd go with a minimum of a Lamotte.
the other stuff you can use other brands etc.
CO2 is the most critical thing and the worst one as far variation, impact on your tank, algae issues(90-95% at least), rate at which is can change- NO3/PO4 are rather slow, even Fe is slow in comparison, and fish deaths.
Yes, more folks kill fish with CO2 than any other single thing they add in this planted hobby.
Ironically, very few folks focus much on CO2 and testing it carefully.
All the nutrient testing for NO3, PO4 will not matter one bit if the CO2 is loused up and pH/KH tables do not get you that far in many situations.
So keep that in mind before running forth with the test kit like it's some sort of "knowledge" and that you are learning.
Test kits just tell you information(provided you use them correctly and account for errors- most hobbyists do not), how you draw conclusions from that info and rational makes all the difference however.
The latter part is how you learn and gain knowlegde, not by monitoring and testing water in and of itself.
I personally did not get into this hobby to spend a lot of time and $ to test the water, I suppose it's a hobby for some..............
I do more than my share at the lab.
I call it work, not a hobby and it's not much fun to tell the truth after the 178 th sample
I think some think they ought to do it, and would like to know how and gain the experience, this is a good reason to test. But most get tired over time and stop anyway and rely mostly on plants, algae etc as bio indicators, the plants, algae etc are the test kits.
Takes time to learn how, but it's cheap, fast, more accurate and more specific to answering what we would like to know about the planted tank.