I have used the Javac tek mate was ok for R22 not much else. I changed to the javac detek its good for R22 but struggles with R404a and R134a the big draw back is the amount of times you have to change the sensors (£40 a time). I now have the javac detek select, the best one yet really good for R404a and you don't need to change the sensors very often. But as with most of the previous comments, you can't beat the old method of pressure testing.