It all depends on how many events you'll be going to. If you were to buy a full set of tickets it would cost you about £80, so an F-pass (£45) represents a significant saving. If you go to about 1/2 of the events you'll have gotten your moneys worth, if you're likely to go to less than 1/2 of the events then it's probably more cost effective to pick up individual tickets.
The added 'bonuses', if you like, are you get a free Freshers t-shirt, a free cinema ticket, and you avoid having to stand in long queues during Freshers week.