Take the train(s). Much more reliable, more comfortable, quicker.
The bus company reviews notwithstanding, traffic around Milan can be choking, leading to huge delays. If you have a flight to catch and no big time buffer, trains are definitely recommended.
And if you buy Fast Track (in advance) you can get by with one hour prior to departure. No huge lines at security there: https://www.milanomalpensa-airport.c...ces/fast-track
If you have bags to check or need to check in at a counter, check your airline's cut-off time, which is less than the three-hour recommended time.