Easy to install? - It depends :-)
I have not used a
SEO contribution... but for
contributions I've used.. some are fairly easy -
just copying new/revised php files while others may
require some changes in the php code that you have
to enter and/or chnage in database sql.
You are using a fairly un-modified osCommerce set-up
so you shouldn't have to worry about how any
contribution will change your site.
~Roland