Can you describe the problem with the exhaust? You don't see people riding with no exhaust for all the reasons above. The same people who posted above would be willing to help with the exhaust problem. Welcome to the forum!
Not to mention the risk of fire on decel and what it might burn on bike.....Both internally and externally.
If he liked bike before he surely wont after a few trips riding to work. Very bad idea.....
Even running with just header pipes isn't a good idea, many of the same problems, too lean, too loud, maybe flame, make the investment in something that works.
If there is some sort of problem with the slip-ons, he can leave them off and run the engine as if he were running drags. Works a bit better with cones in at the heads in front of the pipes, and will need to add a bit (may be a lot) more fuel with that free an exhaust circuit.
Me i don't care if he runes his engine, :bigsmiley6: If he wants to run without pipes then the faster the engine swallows a valve the less time he has to annoy the 99% of people that won't give a rats tail if all bikes were taken off the road.