Hopefully the individual 'parts' of the fly shuttle route will do well (assuming Flybe provide a reliable and punctual service) and any passengers staying on over a stop are seen as a bonus.
SOU-JER is well established and presumably just the transfer of 3 of the 5 weekdaily rotations from the 'normal' schedule.
SOU-LBA there is a market for it, but Flybe did not make it work in the past.
LBA-ABZ is quite similar to the above, and both will face competition from Eastern (assuming they don't just back out).
Outside these ABZ-SOU via LBA is again served by Eastern, and Flybe should be able to stimulate additional demand by undercutting them significantly.
LBA-JER via SOU also is a fairly convenient option as it effectively offers a 3 daily service from LBA, which would not work by itself.
I doubt many people will fly the whole route, although it would be interesting to see the figures once the route has started.