Hi! I've not used them, but not heard anything bad either.
I'm looking at a 'second hand GFS Pro Event' right in front of me right now - I'd gladly stick it in a box and send it to you for 50p! I HATE IT! It's not mine, it belongs to Paul who I live here with, it's HIS saddle for HIS horse - thing is, HE doesn't ride HIS horse...I do - and I refuse to use HIS saddle! And he won't sell it, because he says it's really comfy! Mmmmm!
It's DEFINTELY worth trying several different saddles before you buy! Remember, it's not just essential that it fits the horse correctly, but is also essential that you can ride for more than 2 minutes without having a very sore b*m! .....As I have discovered!
I will ask my saddler/master saddle fitter friend in Suffolk if he has any GFS Pro Event saddles second hand for you, if you like. He usually has at least one or two in at any one time - what seat size do you think you need, and do you know if medium or wide would be best fit, as I'll happily phone my friend and ask him for you! He's a great saddle fitter, and travels about with his loaded van, but sadly doesn't travel as far as you!