The futsal forum is a lonely place so you might not get much joy. I am reffing outside the UK so i can't comment on the course or "worth". Personally, round my way, futsal is tough because it is popular and therefore mixed ability and mixed understanding (including my colleagues, ahem, and sometimes mice elf). There is a lot to learn (counting, dangerous vs non-dangerous sliding tackles, awareness of GK slides, use of the hands), there is quite a bit to the signalling (counting, foul after advantage) and a few extra steps to concentration (GK 2nd touch, movement with 2 refs, checking cumulative fouls, scorers and assists with timekeepers etc.)
I really enjoy it, mostly because you have to be sharp and it can be a real cauldron - if you can handle the emotional intensity of a heated futsal game it is very good practice for the 11-a-side. I also run enough to work up a sweat so I don't find it boring at all.
Definitely worth it.
You should look for a Futsal conversion course and there should be plenty of opportunities in the Surrey/London region for games and experience. Level 6 is the entry level and you move to Level 5 after the usual 6 game process. I moved up to level 4 after a solid first year doing some local Futsal 5 leagues, BUCS games and a handful of National Futsal league games. This season, I had regular NF games in Division 2 mostly but also in the Superleague and FA Futsal Cup. Hopefully, this will lead to promotion to Level 3. There's opportunities at all ages, male and female.
In the UK, the better refs would appear to be English although it's arguable that Wales are the best side and if they continue to improve so too will their referees. I don't know much about the Futsal programmes in Northern Ireland and Scotland.
England has at least 2 FIFA officials in Marc Birkett and Peter Nurse and I think Wales has one, Valentin Ciuplea. Marc is a world class Futsal referee having refereed in the 2012 World Cup Final itself. Karoly Torok is another former World Cup final referee who currently resides in the UK.
You can make good progress in Futsal and in might indoors, warm and dry but the pace of the game can be sharp and demands focus.
Go for it!
I've done it and really enjoy it though it's worth checking what games are in your area before doing the course. I've done a lot of youth games and one exceptionally enjoyable BUCS game. I'm always amazed watching the club and international games on TV at the reluctance of the refs to give any fouls. It's almost as though they don't want a 10mtr penalty to ever be seen on TV.