In terms of comparing the Jock Lowe scheme with HAL's own scheme the payback period will be the same - it's just that the level of airport charges will be different for the two schemes. The Davies reports show that airport charges would peak at around £31 for the HAL scheme compared with £29 for the Lowe scheme.
Fairdealfrank is right to point out the mutterings over patents, but given that Jock Lowe is over 70 I can't imagine he would want the negotiations to take too long!