OP: I have a 20 mile commute that I do one-way with my Brompton in the same way you're proposing, with public transit (and about 1.5 miles of slow, non-sweating biking for one bus link that's easier just to ride) the other way. It's great. It's not as comfortable or as fast as my other bikes, but it's great fun to ride home, and it's not uncomfortable.