A bit of info regarding Young Boys.
First of all, they play on artificial turf, that always deserves a mention, as it is an advantage.
Second, they are the type of team that is well-equipped to batter lesser sides (hence their domestic record), but are really not well suited to playing against sides better than them, with the reason for this being that they are far better going forward than at the back. Think of non-peak Arsenal under Wenger, well, that's the type of mentality they have.
They lost their highly-rated boss Adolf Hutter (pronounced Adolf Hitter - cannot make it up) over the summer. His replacement, Gerardo Seoane, has a grand total of nine months of senior coaching experience, having started his A-team managerial career at Luzern in January. He has done reasonably well so far, but the CL group stage will be his biggest test.
They made the group stage after beating Dinamo Zagreb 3:2 on aggregate. Dinamo, who are the worst they have been in years, lead the return leg 1:0 and were in control, but then self-combusted and conceded twice in three minutes to go out. Other than the two chances from which they scored, Young Boys created nothing.
Players to watch are Guillaume Hoarau (a poor man's Ibrahimovic), Miralem Sulejmani, Moumi Ngmaleu (who could both do job as wingers at sides such as Burnley and Huddersfield), Roger Assale and Kevin Mbabu. I expect Assale and Mbabu to move to better leagues - the former is a skillful and pacy striker, the latter is a right-back who is far better going forward than defending.
I will once again repeat my point about Young Boys not being equipped to face stronger teams. They are pretty mediocre at the back and are not that good at counter-attacking. The central midfield is also not very good and, if United try to play "the new way", which was first seen against Tottenham, they should have no problems winning this.