I use a milliamp meter inserted in the coax behind the receiver so I can see the ku motor move. Installing this meter into a running or working fta system does not have any effect on the signal that I can see. Weak signals are still weak and strong signals are still strong.
Of course there are losses anytime something is inserted between the receiver and lnb, but most lnbs have around 50 db of line amplification which more than covers the loss of inserting this meter into a working fta system.