I can forsee half of the so-called "mentors" putting minimal effort into fulfilling their side of the arrangement: being incredibly hard to contact originally, being incredibly unresponsive to the mentee, being disrespectful of them, being late to the agreed time, only doing one session in total and not making time for others (you really want to help someone improve, you do more than one and you spread it out over time). You saw what happened after i49, some of the donators got fed up of the people who promised to do a few tiny things in return for a free trip to Europe - These guys are playing for like a couple of hundred bucks (maximum each) if they win for a 4 month season (if you include the time practising pre-season) in which you will spend 5+ hours a week practising, you add that up it's a small menial amount for the amount of effort you put in.
Not saying I am against the idea or that getting money for doing something you enjoy is a bad thing, hell no. And at least half of them will do everything they promise and possibly more. But people are naturally lazy, they will promise one thing and fail to deliver, especially if they do not even get something for it. I hope UGC enforce some sort of rule, do all of the perks before distributing money so they can control it if someone fails to deliver.
Also mentoring as a perk insn't the greatest one, I done it loads of time and it is equally frustrating if you can't find the right mentees as if you can't find the right mentors. I'd do it (for free) but I choose not to put my free time towards it at the moment, other things take priority.