I have used this retweet system for a couple of months with reasonable success. It does what it claims.

We don't want to constantly have to share our credentials so this is a nice option for us. However, we don't have enough experts on our team who can contribute just yet. You can approve tweets though so we can intervene with the negative ones.

I love that with GroupTweet, I am able to have many contributors on a Twitter account without having to share the password or risk having the account become compromised.