Of course it is always better to practice off grass, however this is not always possible especially in the Uk winter so we have to use mats.
My only suggestion is when using mats use a very small tee just to raise the ball off the mat to ensure ball "mat" contact, I restrict myself to 5 iron to woods off mats because you would take less divot with long
irons and woods.
It's always good practicing hitting driver of mats. (using a tee of course).
Ian.