I got burned once with a windows phone Omnia 7 as an early adopter and it was beyond useless (lack of apps/configurability) so I will definitely not rush again on unproven phones despite my interest in Ubuntu. Also the price/specs on this phone is horrible compared to Xiaomi Note 4G (190euro) which I own and can recommend to anyone. I hope Ubuntu phone catches on though. Competition is good.
However, it looks like you should be able to get Kitkat on this easily[1].
[1] http://www.bq.com/gb/products/aquaris-e4-5.html Search for "android"