2010, I was a Cadet CSM at Vernon ACSTC for the summer. We (the CSMs) wore our berets and "garrison dress" (Standard dress for all Staff Cadets in Vernon: CF Green shirt, CF green pants and combat boots with pants bloused and rank brassard on right arm - this order of dress didn't exist and I tried to get that changed as a C/CSM... but the Camp RSM and DSM [both RegF] were pretty dead set on making non-existent made up orders of dress and non-existent made up pace stick drill movements the "camp standard"). CSMs however wore sword belts (never used swords on parade since probably the '90s, I think the reason for wearing them was of 2 things: bling and "stand out factor" and the fact that the award for Top CSM is the 8th Recce Regt Sword of Honour Award).
Several things wrong with all of it, but any attempts to make rightful changes were swiftly shot down. Oh well, I would just smile and nod afterwards.
Our berets, if you look here:
http://armycadethistory.com/Vernon%20photo%20gallery/VACSTC_2009_Daily/CMWO%20Geoffrey%20Ravenor%20Sword%20of%20Honour__sm.jpg, as a CSM the cap badge is simply the RCAC crest and banner and the reason was that everyone who was on course or Staff for the summer belonged not to 12 Svc Bn or a Signals squadron etc... they were members of Vernon. 2010 however, the berets and badges were on back order so the 5 of us CSMs ended up going a summer wearing our own unit identifiers (which I personally was indifferent about - not happy nor disappointed - I got to flaunt my Sigs cap badge, yet the colours in the beret and badge faded soooooo much from the sun).
The only exception was that cadets (Staff only) from Highland units were allowed to wear their highland dress... even on the grad parades of the course cadets (which I disagree with because it drew attention away from the course cadets graduating and focused it on the Staff Cadets and their fancy accouterments and highland dress).
The beret is only practical for when you're on parade or at the unit (or a Camp C/CSM when basically your job is to walk around and look good ;D )
And you should also note: Sea and Air cadets aren't issued a beret like Army cadets are, they only get it IF there's supply, and if their training permits. Most Air and Sea cadets go their whole 7 year cadet career with just their traditional headdress and the only time they ever get to touch/see a beret is when with their Army counterparts - and it should remain that way. You want a beret... join the PRes or RegF.