Did my MSc at Cranfield.
Would recommend this rather than city purely because of it's reputation.
Completed the cse part time in just over 18 months flying full time long haul during the period.
Due to the work load involved, and cost only bother if you intend to go into management. £30k buys a lot of holidays.
Also be aware that in many airlines Flt Ops management is very much about time in and politics. The MSc does guarantee you advancement but it will give you a very broad view on areas such as finance, marketing etc.
An MSc, or MBNA are much more useful outside of Flt Ops if you decide to move to another department.