I made a return trip from Birmingham to Manchester last weekend.
Last Sunday it was on the M19 departing Birmingham at 10:10. This was operated by McLeans H 24 MCL, a 49 seat Yutong, in McLeans livery and an "on hire to Citylink" slipboard. Have got to say the legroom on this wasn't great, so if Flixbus is the same then that is probably another reason not to use them. Departure was on time with around a dozen passengers on board. We had an early arrival at Manchester Airport so after waiting 10 mins it was onto Manchester City Centre. For some reason we were going through Piccadilly Gardens, which seems an odd choice to me when it is open, never mind now whilst the road is closed! We were a couple of minutes late into Shudehill.
Tuesday was the return on the M11 departing Shudehill at 16:20, operated by Stagecoach 50503. We departed on time but the scheduled time to get to the Airport is impossible, so we were 20 mins late departing there, getting to Birmingham 40 mins late. We were about half full leaving Manchester, with even less on leaving the Airport.
The scheduled time for the afternoon journey is 2:10, which just isn't enough. The National Express service departing Chorlton St at 15:45 is given 2:45. Far more sensible.
Apart from the lateness of the return journey being annoying and entirely predictable, I was also put off the experience by the "quality" of fellow passengers.
Overall, very meah.