I use the alk, calcium and occasionally the phosphate checker. I like them because I am not good at watching things change color and deciding when it happened. I also find it easier to use pipettes rather than the syringes they provide.
I use the Alk and although it may read up to .5 dKh lower/higher than some other tests the only thing I am concerned about is stability. I run the test 3 times and it will often say 8.5/8.4/8.5 or something similar, but as long as I get the same number 2/3 times I'm happy.
I use the phosphate one as well, regret not getting the phosphorus instead.
For Alk - my day to day test is the hanna checker and I will occasionally confirm with salifert.
For P - I use Phosphorus ULR checker. In regards to which checker is better, it really depends on your tank or tanks. The difference between them is range and accuracy at low levels. If you are running low phosphate tank(s), the phosphorus checker is more accurate less than 0.08 ppm. If you have higher phosphate or multiple tanks, the phosphate checker will provide a wider range.
Technique and following procedure are also more important when using 'checker' type kits. BRS has a very good video describing the difference between meters and also some very good suggestions for obtaining consistent and accurate results.