The feature of multiple recipients at once, it's easy to use as you can add your friends into one email which will be sent together with other members in that group instead having each member send an individual invitation through their different accounts etc.. I dislike how some groups are not so big (e-mail limit) but this doesn't bother me much since most people would get what they need from those smaller emails anyway! Great product - very user friendly especially if used by non techy usersβ¦