Paid plan include: white-lists of posters, custom stop-words dictionary, pre-moderation, tweets archiving, custom logo and other features.
Price of this plan — $50 per month.
And yes, basic functions are still free.
Bad words filter + custom dictionary: use automatic filtering of tweets containing stop-works from default and custom dictionaries.
Ban spammers: use automatic filtering of tweets from users blocked by you.
Pre-moderation: approve tweets to be shown on wall.
Tweets archive: all tweets from your events will be archived.
Audience archive: all members, who will send tweet during event, will be listed for you in report.
Show photos from Twitter, Facebook, Instagram, Pinterest and other networks.
Multi-tags: use up to 3 tags on one wall
Design customization: use your own logo for wall for hash-tag. Everybody in the world who will try to broadcast wall with your hash-tag will see your logo