For DEFO the answer is YES, and yes of course they need you but be aware that your Upgrade can be really hard. Also it depends of the base you are, there are very good professionals that try to help you and motivate you for the CU. BUT I found some TREs in Stansted and some BC that is just the opposite. So if you are so lucky that you have a nice BC and TRE in your base is easier if not you are ....
Also when you try to analize the situation or make some questions in order to improve your weaks areas, you gonna receive ambiguous answers. So you don't know how, when and why...
A part of that the problem that I'm worried it is that getting a base in your country once you have passed the interview before to join the CU course is being really harder, as DEFO no problem for that but once you go through the CU interview be prepare for going outside. Now, they are offering mainly bases in Eastern Europe, south of Italy, Greece or Morocco. And the worse part is that you have to sign a bond for 2 years for your training. So my motivation is falling down very fast