In my opinion a larger tyre has only benefits if either the rider or the motorcycle can use it. I think in general a 130 has to much grip for a 125(134) I rode on my Maico 500 a 120/90-18 Trelleborg tyre, now a 110/100-18 also Trelleborg.
Compaired to a wider tyre I find that I can play more with the bike especially coming out of corners, more stabile. The bike cuts through spurs better, with a wider tyre it always wants to climb up on the sidewals.
Just my thougths, but if your friend has the wider tyre mounted, why not try his bike?