I'm sure the fact that there's more margin in puFoam and its cheaper didn't sway the op's buying process
The price differential is pretty small, actually, and both are well within my budget. As it happens, while I have ordered the carpet & fitting services from a carpet shop, I haven't ordered the underlay and gripper yet - I'll do that tomorrow. I probably will go for Axfelt 65 in the expectation that it will be longer-lasting and more resilient. I really don't like the PU stuff: it's lumpy and feels cheap. I expect it is widely recommended because it IS cheap (a saving NOT passed on the the customer).
The house has suspended timber floors downstairs, with underfloor voids freely ventilated and therefore prone to being cold. The insulating properties of Axfelt are attractive, and if I use it throughout (sitting room, landing & stairs and bedroom) I will have no waste from complete rolls, even though it is over-the-top for a guest bedroom.
All the floors are timber (there's just a small section of concrete where there used to be a fireplace in one room - I'll use hardened nails there, I guess) the skirtings are conventional timber and nailed to the walls. I've no intention of touching the stairs, but putting down gripper and laying the underlay in the other rooms should be straightforward. I've been a householder for many decades and have had carpets laid many times. No fitter has EVER looked at existing gripper and complained that it isn't the right sort, isn't the right distance for the walls, or suggested that for my 'new' carpet I should have anything different. I won't buy it from B&Q, but the stuff they sell is (comparatively) cheap, and looks exactly like any other gripper I've ever seen. There are marks on the floorboards where the old gripper was, and I'll put the new stuff in the same place. I confidently expect that the fitter will pass no comment whatever, but just get on with the job in hand.
The carpets are all polypropylene on conventional (but presumably man-made) backings. They were chosen to be as similar as possible in look and feel to high quality 80/20 wool twist.
Would ANYONE care to suggest the ideal gap between the gripper and the skirting?