Meet & greet everytime. Any substantial traffic to get onto the campus you'd have to get through anyway as all the official longstays are more or less on site. The unofficial ones are typically at least 10 minutes away, not too much of a faff out, but waiting for a bus on the way back is a PITA.
I use the M&G probably 5 times a year and always find it excellent, even for weird requests like flying out of one terminal and back to the other. getting to the T1 one is a bit weird if you don't know the airport, but so long as you pay attention to the signs you should be fine.