I've used BB for ever and the HUB was the best part of it. Recently I added a Nexus 6P to my lineup. I installed the HUB and other BB features. When properly configured, having all my email accounts, texts, BBM, WhatsApp, Instagram, Twitter, etc., etc under ONE app and bundled up the way I am used it, is a joy. For me at least, having all that under one app is key.
However in an actual Blackberry device, the Hub is ever-present and it's your default window. It's not an app that runs like it does on Android. So at times it does not feel as smooth on my 6p but lately it's been very good and I have "adapted". Also with the update to android 7... I can no longer receive BBM pictures... some sort of issue, I get a blank dot. I am sure that will be addressed.
Anyhow once I configured it, it took me a while to get it set up, and had to disable all other email apps, etc and notifications have to be handled only from the HUB.. and, at least for me I also use the BB "launcher", it's "almost" as good.
When I first installed it was free with no nags or ads. then lately they started to mention a subscription. I thought it was simply ads but mine actually said my trial period was over. I could not access anything. Broke down and paid the 99 cents or whatever it is monthly for it to work properly.
Again if you were an original BB Hub lover like me, it's worth your time when properly configured. To be honest before installing, I had Gmail on hangouts. I never used hangouts so I can't comment on that.