I think it is good marketing to BA allowing miles to be used to select seats. However, I suspect BA's accountants may prefer the cash. Compare £20 to the cost of the ticket before taxes and fuel surcharge; BAEC members may find that they may need a lot of miles to book the seat which in turn will create more PR problems for BA.

It is a bit like the benefit to Gold cardholders, you can get a seat where all the redemption seats are taken provided you pay double miles (unless you are GGL where you get one free joker a year). I suspect this option of choice has not been used very often.

VS allow miles to be spent for booking a limo transfer but then you cannot buy a limo transfer by cash; only by booking a C or J ticket.