I bought other microdrippers from Gardena for my tomato plants because even 4 of the ones supplied per plant were not enough. I have installed the adjustable and pressure compensating ones. These are adjustable from 1-8L/h, the ones supplied only give 0.5L of water per hour. I had my doubts at first, but so far it's working. However, I can imagine that you can't install as many as you want before the water pressure is no longer sufficient.

I have two thuja in one pot each that I water with this system. To make sure they get enough water, I have installed three of these Micro-Drippers per pot instead of one.