This thread is getting heated but I'ill try to remain neutral.
Like the others said, just-cos is very dodgy and non-universal. Fire-support and airsoft world are the only ones that states they accept just-cos. I have never used just-cos because VCRA doesn't count cosplay as rennactor.
The expense of playing three games as a beginner is absurdly high, it's huge turn off for people without some sort of income. I understand airsoft isn't cheap in general but the price for playing in sites have some room for improvement. Also, UKARA only last for 12 months, 2 of those months is spent waiting to be approved. If ukara lasts for 2-3 years then the expense would be justifiable, but reality is that it isn't.
If the expense is too unbearable or u felt that u won't play enough games to get ukara, there are less dodgy methods to get RIFs than Just-cos.
Military vehicles trust is a bit more universal and is accepted as a rennactor defence. It's the defence I personally use. It worked on:
-Patrol base
-Fire support
-airsoft world
-Fubar bundy airsoft
-Others