I use the web app on iOS. Feature parity is 100% for me because I don't use push notifications at app on Twitter. The performance is a little worse (mostly touch targeting is not as good) but once you get used to it it is not noticeable. This is an acceptable tradeoff to me because it allows me to block almost all promoted tweets with Safari content blockers. I also think the Twitter native app may do devious things that are less likely to be permitted by Safari.