I’ve updated my E7 to 5.1.1 from 4.4.4 and the results are great. UI are more elegant looking, The performance are also improved, Such as Multi-tasking with ~ 0.3 response time vs. 4.4.4 ~ 0.7avg. response time. Battery life is quite similar with the Kitkat with small improvement.
Transitions and more settings improvement are plus. But there are too many options available nowdays in market I will suggest to go for other options as well