20Mbps upload, wooop!
With 4k streaming using the less bandwidth hungry x265/HEVC codec, the actual needs for higher speeds is minimal. Even in a busy house with six people gaming and streaming at the same time, 80 and 100Mbps is more than enough.
I suspect an average person who uses Netflix might see an advert that says 300Mbs is good for streaming so will be fooled by PR in to getting it. That and people suffering buffering or congestion who get upsold the connection saying it might sort out the issues...
If you are in the right area, Hyperoptic offer 1gbit and telephone line for the same price as Vivid 300