I know you have a lot of responses to this but let me put in my 2
cents.

I recently completed a redwood english garden bench out of clear all
heart redwood.

I would recommend an oil finish as it can be easily renewed on a
periodic basis as it is absorbed rather than a film and thus does not
need to be stripped off.

I would not recommend film finish (varnish, (poly)urithane,ete.) just
because it is a lot of work to strip off the old when time to refinish.


With oil, just apply a new coat every 1-2 years depending on your
environment.

My conclusion after doing my own research on the best way to finish
redwood for outdoor furniture use.