I've used them on a 4m Avon with a 40HP - the set up was very stern heavy, - console with, rear bench housing fuel and battery. Took ages to get on plane with boat on a very steep angle. The doelfins made a huge and positive difference in that case.
It will depend on how your craft is set up, if it gets on the plane quickly and is stable I'd say don't bother.
Member of the Macmillan Round the Isle of Wight Club