I admit it, I spend far too much time on Facebook.
My favorite iPad Facebook app was Friendly. Was being that it has serious problems that haven't been fixed. It seems that the developer is more interested in the desktop version and a Pinterest app.
But I went ahead and gambled the US$4.99 and bought the mac desktop version.
In a nutshell, it is little more than a wrapper around an HTML browser, meaning that you get the same page you would if you'd used Safari.
The wrapper gives you a nice sidebar mode, the pictures zoom larger when you mouse over them, ads are slightly greyed out if you choose "Enhanced Browsing Mode" and you get drag and drop for photos and links. Basically $1 per feature. However these are mostly things that may be added to your web browser by free extensions.
Is it worth buying? That's up to you. The most useful feature is the side bar mode where it takes up maybe 20% of my screen on my 17" MBP.
Would I buy it again now that I've used it? Nope. That's probably why there's no "lite" version.