I agree with you about 12A. It appeared out of the blue and had we known in time, we would have asked for better quality materials.
For myself, I don't dispute that good quality materials have been used for 14A Wyleu Street and I'm glad that you, at least, don't find it intrusive. However, I really can't see it as complementing the rest of its immediate neighbourhood, and it is effectively a new building rather than an extension.
HOPRA is concerned that this will mark the start of an influx of people who will then dig out basements or build other intrusive add-ons, causing years of disruption for neighbours here and changing the character of the streets in a messy and unco-ordinated way. A lot of this is now happening in Clapham, for example, and North London is full of stories of neighbourhoods undergoing years of turmoil and uncontrolled alteration to local streetscapes.