I've been using API kits for NH3/4, NO2, NO3, GH, KH, pH, and phosphate. It took some time to get used to interpreting the colors, but now I can get a good feel for where things are going to land after 30 seconds instead of waiting the entire 5 minutes (for some tests). All in all I've been pleased.
Since I got past the initial cycling on my two tanks, though, my most frequent testing is for nitrate (NO3). The API kit involves two reagents and 1 minute of "shaking". Not a big deal, but kind of a PITA. I'm considering trying the Seachem Multitest NO2/NO3 version as in seems easier to implement.