Hi, I get master test kits, then only replace the test I'm out of, over the years I have used different ones. I used Redsea in the beginning, that's what the store carried, and I never had any trouble with it. However, I was told by everyone on this site the kits are not trustworthy, so I switched to API, which they all recommended back then...which now I have discovered are reading super high on nitrates, which caused me to seek yet a different brand.
I use ammonia test strips, I don't care about the brand...if I see any ammonia it means do a water change, the number does not matter. It's the only test strip I use. The ammonia tests for API, Redsea, Seachem etc...etc...etc...all have a wait time, strips are instant, and numbers don't matter..
The Master kit I liked best was Instant Ocean...it came with colored tiles that sits next to the test tube to be able to read the results, it was so easy to match up the color and read the results. All the other kits rely on a card that was printed out. The colors are so close when trying to read the results, and the cards color varies because it really all depends on the ink in the printer when the kit was packaged. Unfortunately, I was forced to change brands because the replacement packets were hard to find of, not even on-line, every place was out of it at the same time, so I had to purchase a different brand. Once I began using a different brand of master kit, the replacement tests had to be of the brand I had purchased, it's a vicious cycle.
So now I buy SeaChem... all the tests come with a regent to be able to double check it, to be sure that the readings are accurate.
Oh, and the replacement tests for Instant Ocean, I didn't have to buy the colored tiles or tubes again, just the tests crystal packets...