Personally, I prefer the Doel Fin. It was the first on the market and has been copied but not duplicated. After having over 50 boat year's experience on multiple boats I won't own a boat without one.
The caveat is that performance on an I/O is iffy, and to optimize the performance on an OB the engine must be raised so that the AV plate skims the water on plane. All the urban legends about AV plates breaking off, collecting trash and losing top speed are only true for those that don't set up the fin correctly.
Yes, it will definitely help. A 4-blade with stern lift may help too, but that approach is not comparable.
Talk about Chevy vs. Ford, or 'Rude vs. Merc and you will hear arguments. But no topic will cause more controversy than the "fin". I can only relay my own personal experiences, supported by real data.
My current boat came from the factory with awesome performance. Nevertheless, the Engineer in me made me want to customize it. An Enertia prop, a Doel Fin and an adjusted motor height reduced my prop slip, increased my fuel economy and added 3 mph to the top end. When the throttle is punched the boat comes on plane with not even a hint of bow rise. Certainly, the package accounted for the improvement, but the fin was an integral part.