This article is from the Boats FAQ, by John F. Hughes with numerous contributions by others.
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.