My outdoor cat has worn a break-away collar for 17 years with no incidents or issues (obviously, not the same collar for 17 years!) You need to test the collar yourself by hand and when it's on the cat's neck to assure yourself it will break off. My favorite brand, both for ease of break-away and effectiveness, is Rogz.
I have a friend in Arizona who has two cats. She never got them collars/tags because they are "strictly indoors" and will "never get out". She was positive they would never, ever get out. Then, one day, her brother opened a window, and the male cat tore the screen out and both cats got out. The younger female was not vaccinated. Luckily my friend found them both quickly, but she could have lost both, or had a VERY sick kitty if the female had gotten exposed while outdoors.
Another friend also had a "strictly indoors" cat who would "never get out". My friend never put a collar on her, nor did she have this cat spayed because she was so convinced her cat would never get out of the house. Of course, the cat got out, and was gone for two weeks. Luckily a neighbor ended up finding her and returned her, but by then the cat was pregnant. She had tons of complications to the pregnancy, including needing a C-section and infection, and one of the kittens died.
Both of my friends were very lucky that they got their cats back quickly after they escaped, but it's not the typical experience, unfortunately.
So, in my experience, "Oh they'll never get out" is not an excuse to collar and tag your cat. You might be the most careful person in the world, but if you have other people EVER coming into your house, that's a risk. Plus cats are lightning-fast when a door or window is open, and will literally teleport outside before you can get it closed.
The collar CAN be a scary thing, but honestly, I think the risk of a GOOD, high-quality breakaway collar NOT breaking-away is very small. If a cat is able to strangle itself on its collar before the collar breaks, I feel like there was probably some defect or too-tightness that could have been detected if the collar was extensively tested before placing it on the cat.
Like I said, my cat has worn breakaway collars her entire life, and she is an outdoors cat. She has lost a few - maybe 3 - over the course of her life. Right now I prefer this brand:
That's not the exact one I have, but you can see that it has an ADJUSTABLE breakaway strength. I use the "lightest"/least strength setting.
I also have two different tags on the collar, but that's because she's outdoors and I'm paranoid :}