This is an operation from one regional airfield, pretty much, in the middle of nowhere with minimal navigation aids, poor public transport links etc. to another regional airfield, pretty much, in the middle of nowhere, a regional airfield on one end of the route might be OK as long as there is a designated city airport on the other end of the route, this has regionals at both ends of the route!
Phileas, in fairness to Shoreham it has the first GPS approach to a GA airfield in the United Kingdom as well as a perfectly good NDB approach - not too short on navaids. Bearing in mind that a 2 minute shuttle minibus will run from the airport to Shoreham-by-Sea station, which is 13 minutes from Brighton by train, you've got a Brighton-Shoreham Airport travel time of 15 minutes which is considerably less than the alternatives, weighed up in time terms:
By air
Brighton - Shoreham Airport: 15m
Check-in/security: 30m (generous)
Flight: 1h
Immigration/customs/baggage collection: 15m
Pontoise Airport - RER (A) Cergy –
Préfecture: 15m
RER (A) Cergy –
Préfecture - Charles de Gaulle-Etoile (Arc de Triomphe): 45m
Total time: 3h maximum
Total cost: £150 return inc. transfers
By train
Brighton - Ashford International: 1h46 minimum
Transfer time: 20m minimum (cutting it a little fine)
Ashford International - Paris Gare du Nord: 1h53 minimum
Total time: 4h minimum, often 5h
Total cost: £99 return minimum, often £138 return
So there are some clear advantages.