Performance on my desktop PC with good internet connection is really good. Even working together on something is seamless.

Opening my shopping list on the mobile app that takes like 5s to start and another 5s to load due to bad connection... not so much.

Their no-offline implementation is starting to bug me more and more and I have moved away from it for a lot of things.

I still really like their clipper addon, though. I use that to rapidly store articles I want to read later on desktop and mobile Firefox. Storing is fast and retrieving is fast enough if I have time to read an article anyways.