What is the point of the mates deal when the latest offer is better

[#1]

As per the title - the present £5 offer is better than the best mates deal - really needs looking at

While I am posting why can't I set the price cap to zero

[#2]

as a follow up from this

if I sign  up to the offer on the website now can I change to a mates rate if a better one comes along