I haven't needed to use the adapter for filling - yet, but I used the adapted funnel nozzle to allow the adding of some diesel injector additive.
Having said that the filler neck has an abrupt bend just inboard of the "easy fuel" shut off flap. If you push the adapter too far in it will restrict the flow rate (I think) and with the high rate pump splash back will then occur. I'd suggest only inserting the adapter nozzle just far enough to get the fill neck flap out of the way, and go light on the bowser trigger.
(And we'll have a mod on our case if we are not careful here
)
Cheers