1. Having never owned an Android TV TV before, all of the doom and gloom I was reading made me anticipate it being really slow and laggy and annoying to deal with. However I have found it to be fairly snappy. It's not lightning quick by any means, it doesn't run as fast as LG WebOS3.5, but it's not far behind. The Netflix app loads fast, the Amazon app is a bit slower. When you cast a something it changes input straight away.
The one thing I would say that isn't implemented well, is the youview software. I really like youview, my parents have a couple of boxes and it is great, but it doesn't run well at all here so I would reccomend deactivating youview and using the Freeview Play TV guide. Also if you want to record to a USB HDD like me, you can't do this with the youview enabled anyway.
2. HDR is great. I watched the netflix original Annihilation yesterday, and the darks were detailed and the whites and the might scenes with specular reflections and stuff were awesome. I used to think HDR was a bit silly because it makes the brightness go to max, but now I get it! Also with gaming it looked really good as well, but I have only played Destiny 2 so far with HDR.
3. The only reason I knew there were black bars, is because I know that films have a different aspect ratio to regular TV. I was truly impressed by how black the bars are, makes me wonder how I was able to put up with the milky grey 'black bars' on my previous TV haha.
4. The o my time I have noticed blooming so far, is when the TV is turning on and there is a little bit behindaround the Sony logo, and then a little bit when the YouTube app is loading/I am casting YouTube, again just around the logo when it is loading up. I didn't notice any during actual viewing of any content so far.