On the cold water line on our plumbed in machines we use and recommend Nuovafima gauges of Italy
The small plastic ones are too small to accurately set or read the preinfusion pressure in our view
This 63mm diameter gauge in 0-6 bar range gives you 0.1 bar increments, which is about perfect
In New Zealand we buy them from these guys, http://www.cps.co.nz/shop/gauges/63-mm-gauges/63mm-brass/stainless-bottom-entry-gauge/P147/C36
Given there are so few bits to break in our plumbed in machines, spend a little bit more on the installation and enjoy the reward of a nice set up for years to come