well £28.99 inc vat is the price difference between buying the ebay item & buying it on a 14 day offer at "trade price"
So for premium of £28.99 I can have upto 48 days credit & pop into my local branch & collect stock or normally next working day if not in branch stock...
SCB can sometimes, very occasionally be of use, I've used it precisely zero times in 20 years!
If I'm ever fitting 2 SABs because of low bell height, chance of attracting neighbours at the back etc... then I just up the PSU.
Yes wireless bell is, well, just that so no settings to worry about.
If you have a single wired bell, SAB is the way to go.