chipping means that you can't use skills chip to either chip your skills onto one to sell it
or insert a filled one to increase your own skills
if you just started it isn't that adviseable you start chipping right away either way, can be kindy expensive and after that you still have to buy your equipment
that you can't chip is the main downside actually, since you don't skill faster or slower
the second is, that your mentor has to release you via his list when you reach graduation level
if your mentor is a 100 pts rifle noob who thinks you get awesome gifts and plans to finance his gameplay with this and quits
you have to write a support case first to be released by MA/FPC (game developers that is)
although, even if you stay disciple a little longer then, you just can't use skill chips, so the disadvantage there isn rather small
you CAN use mindforce chips like TP chips
and yes, its useful to have a mentor and a good soc helps as well, since the mentor can't stay 24/7
having someone who played for longer giving advice can be quite valueable (also in terms of saving peds)
and yes, if you want one, be fast
once you reached 20 points in a graduation skill like rifle, handgun, longblades, concentration, you will be too skilled to have a mentor
as for mentor offer, check my signature
also check my guide, link in signature as well
hf