I took a bus in 2014 (now part of FlixBus I think) from Freiburg im Breisgau to Zurich and back for a day trip to Zurich; I suspect this bus continued on to Colmar. I dislike long bus rides and would greatly have preferred a train, but I booked near the last minute, and by then the trains were super expensive - maybe 3X more expensive. So I took the bus, and it was fine - many long flat stretches of freeways. I took another bus last year that was a FlixBus from Slovenia to Italy and it was 45+ minutes late but otherwise fine - for a bus. I am glad I had the FlixBus app on my phone to get notifications from them that the bus was late but indeed coming - after 30 minutes you kind of start to wonder...
Booking this far ahead? I'd almost certainly take the train if I could get a decent price - probably can - on the train, even if it costs more than the FlixBus. But I do prefer trains, as I said above.