I do not use them, but I do not do a lot of plumbing.
They are quick and easy for someone who does not know much about plumbing. That is their big selling point. However, they require proper prep and proper installation. I suspect many failures come from lack of doing it right.
My sister's house had a leak under the floor during a weekend a few months ago. Needed a 'instant' fix. My son came over to help me and showed up with some shark bite fittings. I told him no, here is a tubing cutter, some braided plastic tubing and hose clamps. Hard to get to place, had him crawl under and install those. When I had time after the weekend, I went down and bought copper fittings and a section of Pex. My son does not know how to sweat copper tubing, so I crawled under with him and showed him how to sweat on fittings and install Pex and clamp it. I know it will last.
Explained to him why I had reservations about shark bite fitting. I have seen several fail or drip.