I wouldn't sign up for a site using FB/Twitter unless there was a solid technical reason to (i.e. Buffer and Twitter, because it's a Twitter-posting app). And

I wouldn't sign up for a site using FB/Twitter unless there was a solid technical reason to (i.e. Buffer and Twitter, because it's a Twitter-posting app). And that's because I see no reason to associate my Facebook (family/friend-facing, lots of personal stuff on there) with any company. I like to keep a strict firewall in there.