Sometimes it's the same line, often it's different but quicker than the normal line. It seems to vary airport to airport, terminal to terminal.
It sounds like it might be more trouble than it's worth with that kind of drive. Yes, the customs lines can be very long (they were when we landed at SFO in August). But I doubt it took people 3 hours to get through them. But GE can save you time for pre-check domestically (MCO especially since those security lines can be a mess). We fly domestically more than internationally, but still like that we have it. For us the interview was a pain - took forever to get our appointments (3 all on 3 separate days), about an hour to get to the airport, paying for parking, etc. But we are glad we did it since we do fly a minimum of several times a year. Only you can figure out what it's worth to you.