Just had mine done Norwich, apparently it's 4 degrees now, smells great too
I can't comment on any branches other than the Milton Keynes one, but they've always been honest with me and never tried to sell me anything.
They will likely do a 'free health check' and try to sell you brakes, exhausts, tyres and shocks mind....
I couldn't say but it's a cheapish way to get a full system test to find out
Does anyone know if they only charge if they can get it working?