Man Utd is playing at home and they haven't been scoring much goals. I remembered seeing a statistic where almost all of their home games ended in 0-0 draw in the first half. It would be much safer to take under 2.5 goals.
Over 80 % of their home or away games mostly ends with 0-0 in the first half. According to the statistics if you bet on this then you will surely gets profit but things could go as unexpected. Recently their performance has been alot better so there could be some goals atleast before the first half ended