It works, but it isn't undefeatable. I used it when I first got my Raven, the entire purpose of that bike was to be a super reliable commuter, for a job where being late caused others considerable inconvenience. No punctures for 8 months, 11,000 km, then a shard of glass stuck in the tyre didn't give the tube chance to heal. By the time I'd come to a stop, there was green slime everywhere, the messiest puncture I've ever had. Examining the tube later, it had sealed 4 or 5 previous punctures. I swapped out the tyres for Marathon Plus next time they needed replacing.
One of the issues with self sealing tubes is you're unaware of it happening, so whatever caused the damage might still be in the tyre and repeat it. There may be better sealants available now, I think Thorn recommend the Schwalbe one. On my utility E-bike, the only repair kit I carry is a seal and inflate aerosol (Vittoria Pit Stop, though there are others) I've never had cause to test it, though I bought it after being impressed by someone else using it. It sounds a risk relying on it, but I'm never that far from home on this bike.
For leisure riding, I'd rather choose the best tyres for riding and accept the punctures, though a couple of years ago I had a spate of them that tested my resolve.