I've had great readings using Tetra Easy Strips 6-in-1 test strips. I've used the API test strips and found they weren't very accurate, so I stick with Tetra's. The KH
and PH are iffy on the Tetra strips, but they give you an idea of what's going on so you can determine if it's worth doing a liquid test or not. So from my experience, using test strips is just fine and worthwhile. Leave the liquid test for when a detailed reading is imperative (i.e. sick fish, cycle out of whack). Just remember to keep your strips sealed in the bottle.