vxl works much better with a 2.4....far less interference, but its not required.  Maybe the esc just needed time to dry out, and by the time your friend got it it had dried.  Cell phones are like that....submerge them in water and they quit working..let them sit for a few days (maybe even a week) to completely dry out and they work again.

Yes 2.4 is a good investment for any brushless......i made the switch shortly after putting the vxl in a b4 from FM to 2.4 and saw a world of difference.