Taxis are reliable but it is a solid 45 minute ride to Jetty from SEZ.
Upgrades are dependent on availabilty but Diamonds are typically pre-upgraded upon check-in at the Jetty.
Never taken helicopter but I am assuming schedule is flexible based on the increased cost.
We usually hang in Beau Vallon area after taking the mid-afternoon Jetty back to Mahe, before catching a red-eye.