I've haven't used Facebook ads at all, but I had a look last night, just out of interest. It looks fairly doable on your own, rather than paying someone else to do it. The Udemy course is on offer for £12. I You Tubed it and there's loads of free info as well.
I used to do Adwords (might do again this year) and once you know what you are doing, it gives you a great sense of being in control of your business advertising (rather than keep phoning other people and asking them to change things).
I am guessing that Facebook advertising is like Adwords; you have to keep tweaking it to get the best out of it. Also I am guessing you can turn it on and off when you wish. I'd rather be in control of that than pay someone else.
Then there's obviously the fact that you'll save £600, but then you will have to invest some time.
Most importantly, I saw your other topic and you are expanding your services. I think once you get to grips with Facebook (and decide if it works for you) then you could do separate campaigns for windows, connies, caravans, driveways etc etc. If it were me, I would like to be in control of all that myself (if you have the time).
You may also consider Google Adwords. It worked well for me, but I am now at the stage where I am compacting my round, so I don't think Adwords is 'specific' enough. Also Google business plus has worked very well for me.
Anyway, just my thoughts.
Good luck.