How safe is it to have my cats teeth cleaned?

Bad breath in dogs is almost always due to tooth problems, and both dogs' and cats' teeth can be cleaned without harming them - just like yours.  The only question is "Is this plaque actually causing the bad breath?"  Dog-breath is evident because dogs pant and mouth-breathe on us.  However, cats don't.  They almost always breathe through their snouts/noses.  So get the teeth cleaned and then check kitty's breath a day later to see if it's improved.  If not, the problem wasn't the teeth.  (It could be lower in the throat, or even up in the snout or sinuses.)

The spitting-out of food is worrisome.  Cats normally drop bits of food while eating because they have no lips and almost no cheeks - but they don't normally bite off more than they can chew and swallow.  Their tongues are rasped to keep food from falling back out.  So what is going on here?  Are the teeth SORE?  Is the throat obstructed?  Is he meowing just as he always has?  Follow up about the food-spitting when you go back for the cleaning.

I have had dental work done of my cats several times and there has never had a problem. Cats acted normal after the anesthetic wore off completely. 

It's safer for your cat than it is for whoever is trying to brush your cat's teeth.  There are treats that promote dental health that should be tried first, for your own safety.  

Five years is very young for a cat to have dental problems.  Get his teeth cleaned because all that crud is washing through his body and will cause illness.  And while the vet is examining his mouth under a strong light, the reason your cat is dropping food may be discovered.