It really depends on the airport. As a US citizen returning to SFO I have spent anywhere from 30 minutes to 2 hours in line.
I am considering signing up for Global Entry.
So, given the procedure (and the non reimboursable fee of US$ 100)and depending how distant you are from an "interview center" (and how long does the interview take):
https://www.cbp.gov/travel/trusted-traveler-programs/global-...
I would say that a "make even" point could be around 3-4 international travels planned per year (given that the program needs to be renewed after 5 years).
For me ... well, I'm an American but I live in Colombia, which generally meant lots of questions and highly suspicious treatment before I got Global Entry. Now I don't have to say anything more than mornin' when entering the country. Totally worth it to me. :-)
Yes, that would probably be the most convenient way.
Mine took 5 minutes at most. The real inconvenience was the closest place to do the interview was a 3 hour drive. YMMV but anything I can do to spend less time in an airport is worth it to me.