personally never used it but what I gather from other forums and folks that have used it (they use it on brightwork not below the waterline):
Its UV protection is based on iron oxide (rust) so it does add an orange color to your wood
Its a seasonal coating - needs to be reapplied every year
Most folks think that it's downright ugly compared to a varnish finish
OTOH
It's easy to apply
It does offer UV protection
for my two cents:
anything that's breathable not only lets water out but lets water in -water slowly going in and out of wood (particularly plywood is not a good idea)
water beneath an oil finsh can tend to mildew and turn black
oil finishes are almost impossible to sand off
YMMV
