A great many people report improved time-to-plane. Some report slightly reduced top-end speeds. Everyone seems to say that installing one may void your warranty, and you should check this out for your particular motor. Many people report installing and then removing fins, finding that handling suffered enough that they preferred the old way. (jfh)
One person with marina experience writes:
Doel Fins. The marina that services our Evinrude said they had replaced several lower units that had cracked from the stress that overcame the newly weakend area they are mounted on. The maria I worked at had no complaints.