The downside to custom chips is the cost. Excluding artist fees, you are looking at 20¢-30¢ a chip for labels on Majestics or other China clay.
The up-side is that your game will be much harder to bring in a counterfeit chip. Someone can replicate a relabeled Majestic chip, but it would take much more effort. So the security measure here is that you are removing the temptation to counterfeit a chip, because of the effort involved.
Obviously, a game with friends will be safer than a game with people you don't know as well. Again, removing the temptation to steal makes the game safer, and friends are less likely to steal from you. However, that temptation may rise if that friend "needs" the money. People have been known to do otherwise inexplicable things when they are deep in debt.
A $1-$2 game over many months may cost a losing player tens of thousands of dollars over a year. It may be just a couple buy-ins a week, but it adds up over time. If the gambler is also losing thousands on the ponies, lottery tickets, or at other card rooms, the temptation may become very high. Custom chips makes your game a little harder to pull off the scam.
So the question is, is that level of security worth 20¢-30¢ a chip?