It's totally fine to use, but it's a pretty big pain to develop for. And you basically cannot avoid it, since it's forced on every single iOS user (third-party browsers on iOS are essentially just Safari with a custom UI due to Apple's walled garden policies).
Safari is notorious for adopting open web standards and APIs incredibly late or not at all, leading many to believe that it's holding back the ability for web apps to achieve more native-app like capabilities on purpose. Right now, some major APIs are not supported on iOS, even though they have been on Android browsers for a while. The ability to install web apps locally and have them send notifications finally came to iOS Safari in a pretty half-baked fashion years after it arrived on Android. And that's just one example of many.
It also just behaves slightly differently & sometimes even explicitly off-spec compared to Chromium and Firefox engines in so many small ways that you quite often have to debug strange Safari-only bugs. It's pretty annoying.