Is Subscribe by Email Scalable In Theory?

My question is simple; once the bugs and corks are taken care of will this plugin potentially replace my third party auto responder? =D

How scalable is it really?

How do you think it will compare to a third party service?

Will the emails go to spam or is it just as effective as a QUALITY AR?

PS. I'm using a dedicated server so I am only limited to the plugin.