Will be interesting to see what happens on the Guernsey route, only had a quick look but it looks like Blue Islands will be offering up to 29 return flights per week (4x daily apart from Friday when there will be 5 daily) this summer between Guernsey and Southampton and 20 per week during the winter (3 daily, apart from 2 on Saturdays) so looks like we'll end up with overcapacity on the route and more seats than what will be available between Guernsey and Gatwick.
Jersey - Southampton however will have less than half that capacity - 22 per week during the summer (x3 daily except x4 on Fridays) and 21 per week during the winter - (3 daily)