The look and feel of Tweetbot for Mac is similar to the iPhone and iPad version of Tweetbot, yet tweeked to be more appropriate for the Mac. The left hand side has a column of tabs that take you to your timeline, mentions, messages, favorites, retweets, mute filters, and more. You can change the size of the window to fit your needs -- from short and skinny to wide and tall. Tweetbot for Mac also lets you open different tabs and views in new columns and windows, including the timelines of multiple accounts, so that you have many screens available simultaneously.
Tweetbot for Mac supports shortcuts and gestures to make the desktop Twitter experience quick, easy, and natural. For example cmd+n will create a new tweet, cmd+r will reply to the selected tweet, a swipe to the right will open conversation view, and swipe to the left will open the tweet detail view. And instead of Tweetbot for iOS' trademark action drawer, if you hover over a tweet icons that let you reply, retweet, mark as favorite, share, and more overlay on top of it.
Now the price. Tweetbot for Mac is $19.99, which is substantially more than the iPhone or iPad version. Unfortunately, during the Tweetbot for Mac alpha period, Twitter changed their Rules of the Road to greatly restrict the amount of user tokens third party apps could use. That means Tweetbot for Mac will only ever be able to activate a limited number of users, which means a limited number of customers. If you have a limited resource and a limited market, prices go up. You can't spread development and support costs, and profit margins out over a huge quantity of users, so each user pays more. Tapbots is pricing according to the market conditions Twitter has created, and they're probably not the last Twitter app maker that's going to have to do that.