I have come to this conversation later but have had some limited experiences with:
Gavin (several dives)
SS (about 8 hours dive time)
In regards to the trigger mechanism on the SS. I didn't find it very difficult to deal with. Like anything new, it took a dive or two to figure out, and then it was pretty much seamless.
My personal opinion is that burn time and thrust is much less of an issue in the open water/lower current/colder water environment that we typcially dive here in Monterey. There just isnt the overall need for a 3+ hour scooter as:
A) Physically staying in the the water that long is difficult due to the cold
B) traveling that far underwater on a single scooter is a risky proposition due to changing surface conditions, need for a boat to find you, posibilities of navigational errors.
Indeed if you look on the boats, primarily people are bringing either X-scooters or smaller Gavins.
For shore diving, we typically don't have to deal with a lot of surf, but having to lug a larger scooter up and down boat ramp (Lobos) or stairs (CRB or breakwater) is no fun.