Has been working great for years here, no bugs to speak of across 3 browsers and 3 OSes. Notifo notifications are amazing. UI is second to none. Flawless local/offline sync, so no downtime ever. Tagging system works great, and it's how I know what to do next all day.
My only gripes are
1) no mobile version (it works on my iPhone, but it's not the optimal experience to have to drag left and right. a dedicated app would be better imo)
2) there's no faqs/documentation/getting started guide/features/nada. No help desk if you're stuck or having problems. Despite all this, it has lots of users still apparently. Contacting the developer valentin shergin (yandex guy) is a shoot and miss. Development seems to have slowed down a lot, but there's some new features popping up here and there. Mostly active in Russian community.