These plugins are great as long as you're sure that everything you're using is sending mail through wp_mail. Not all developers are equally strong on doing things the WordPress way.

A piece of advice? Before you start working on a dev server that has user accounts on it, change all of your users email via MySQL using something like:

update wp_users set user_email = CONCAT("sam+", ID, "@getparka.com");

That way, even if everything gets screwed up, your dev site CANT email your users because it doesn't know who they are.