It is certainly an impressive feat, they all work and perform pretty well. They're doing this to dog food their own engine, mainly the UI side of it. As far as

It is certainly an impressive feat, they all work and perform pretty well. They're doing this to dog food their own engine, mainly the UI side of it. As far as I am aware all apps now use this instead of the native/web stacks they were using before, but its been a bit of a rocky transition. Having used their website for years it just works and is pretty fast (However it is much slower in recent years than it once was), the new in-engine app just feels kinda clunky, its all incredibly slow and janky. Definitely not the smoothest of transitions