Pro Plus is largely overrated. Each pill contains half the caffeine of a cup of coffee, and there is little chance of overdosing (you need about 150+). Also, the long term problems are neglible for a young-student: assuming you stop using them by the time your 40, you should have no problems what-so-ever. The effect each pill has on oneself is largely based on how much of a Pro-Plus mood your in. I once took about 8 and was a bit delusional, but that was because of no-sleep for about 3 days. I once took 25 at once and just felt a bit tired. As I said, most of it is based on how cool you want to appear. I see losers out who claim to get wasted on like half of one.
It will not substitute for sleep. They will make you feel midly ill if you are really tired, but can provide some small boost if you just need a bit of a perk. Most of this is probably solely-psycological.
Incidentally, I didnt find them particularly addictive, even after going through about two of the 96 packs in a fortnight during Year 13 for fun. They are dirt cheap and are sort of fun, I suppose.