Better to suffer the loss of a few safety collars/tags than to find your cat hanging lifeless from a tree limb, hung by his own (non-safety) collar. The microchip (and earring ID, another possibility) are good ideas, but if a neighbor finds your cat without visible ID you may not be notified that your lost cat has been found. The neighbor could just assume it is a stray because there is no collar, and kindly either just feed it outside, or make it his own indoor cat.

Seems to me that outdoor cats should wear both safety collar/tag along with implanted ID to be on the most thorough side in case kitty wanders too far from home. There is an inexpensive tag kit sold at PetSmart for I believe under $2.00. You simply write info. on disc then bake for a few minutes in the oven and it expands to normal round tag size ~ nifty!