@Nogrossi - gosh those are generous upgrades.
Not sure if it's policy, but since Glasgow relocated to the new rental centre, I've had reasonable upgrades (previously upgrades were as rare as hens teeth at GLA).
My two most recent GLA rentals (reserved compact) gave me a Kia Optima (group O) which was far better than I expected and an Audi A3 (group D3) - the Audi might be branded premium but on sport-line suspension the ride was shockingly bad. They've removed the shock absorbers and fitted wooden block - dreadful on the poorly surfaced roads of Argyll.