[TYPO3] Differences between extensions "Front End User Registration" and "Email Address Subscription"?

[Ian Solo]

Hi!
What are the differences between the two extensions:
"Front End User Registration" (sr_feuser_register)
and
"Email Address Subscription" (sr_email_subscribe)
?

I did read the manuals but I can't figure out why should I use one or 
the other one.

I'm used to use sr_feuser_register, then (searching for Captcha 
integration) i found sr_email_subscribe described, in the "What does it 
do" section, as:
"The Email Address Subscription extension is built as an extension of 
the Front End User Registration (sr_feuser_register) extension and 
therefore has very similar features, including..."
Then follow the similar features.

But, what are the differences? At the moment sr_email_subscribe looks to 
me like a copy of sr_feuser_register.

Thanks in advance for your answers.
Best regards, ian