90 Mustang Gt tech question?

I want to install a fuel pressure gauge on my 90 Mustang gt, 5.0 fuel injected. I bought a spectre fuel pressure gauge, after I bought it I read on the back that it isnt for fuel injection, what is the difference between a carberated fuel pressure gauge and a fuel injection pressure gauge, I want to just use the one I got, is it going to do anything negative other then just break or give a false reading?