Hi Graham your bike comes with progressive springs as standard, so they are what the bike was designed to run on. I have Hyperpro progressive springs in mine and Luke R6 shock kits. Had problems with mine to start with , spoke to Luke and he'd spent a lot of time helping me out, but the front settings back from Hyperpro settings to the Yamaha standard settings and very very much improved, will now run and see how I go.Do not give up, I think you're mechanics have got some thing wrong, speak to Luke he really knows his stuf and I am sure will help you out. Good luck.
I would contact Hagon and ask if there are any specific recommendations for fitting their springs to the Fazer and then confirm with the workshop whether what they have don is correct. I know that Hyperpro recommend a 170mm air gap with their springs which is less oil than the Yamaha recommended 140mm air gap. If the Hagon springs also require less oil but the workshop have refilled to what Yamaha specify this could explain why the suspension doesn't feel right.
Hi Graham your bike comes with progressive springs as standard, so they are what the bike was designed to run on.
If you say where you stay maybe someone could recommend a different garage or a more technical foccer could maybe come have a look at the forks?It sounds like that garage is not working for you with all the issues though so i would definitely be looking at somewhere different, maybe a suspension orientated place?
Graham - bit of a ride for you but I always use Sopers of Leigh-on-Sea. Excellent service and decent prices.