IMO, unless you are just starting out in the hobby, test kits for freshwater aren't really necessary. I've kept fish for 30+ years and the only test kit I ever used was for one for pH. Provide your fish adequate filtration, don't overfeed, don't overstock, and keep up with your water changes. Observe your fish. If they don't look normal, change water. If you test your water and find you have elevated ammonia, nitrite, or nitrate levels, what are you going to do? Most likely change water any way.