From the Store descrption (again I'll point out that this is for Windows Phone 8.1 only):
Want to truly personalize your lock screen? Live lock screen lets you choose from 6 new lock screen layouts to add a distinctive touch to your Windows Phone. Each layout has a revamped design for the time, date, and notifications, as well as a unique unlock animation. You can also cycle through multiple background images throughout the day to keep your lock screen fresh—or just get the latest incredible image from Bing every morning.
Here's some of the set-up and operation on my Lumia 930:
Performance on my Lumia 930 was fine, though I've heard mutters around the Interwebs that using Live Lock Screen BETA causes extra delays when unlocking. It's true that there's up to a second's delay after pressing the screen button on the phone before the theme is fully 'assembled'/loaded, but then there was almost as much delay on the native Lumia 930 lock screen (slower than under WP 8.0 on older phones, in my experience).
'Themes', as Windows Phone applications, do have some knock on implications, which some will complain about. In order to 'show' your Start screen (or whatever was in the foreground when you locked the phone) underneath its animating panel, Live Lock Screen BETA takes a screenshot of it at the time of locking and then uses this as the background for the unlock process. If the interface was one which was itself 'live', e.g. a news ticker or clock or similar, then the content will be out of date until Live Lock Screen BETA has fully been swiped away (and closed), at which point the screen will come bright and the content will refresh.
Secondly, depending on which application was in the foreground before the screen lock and its status in terms of playing ball with WP 8.1's multitasking, you may get 'resuming...' before that application reappears.
These minor glitches will hopefully be resolved through Live Lock Screen updates (including the removal of the BETA tag) and through other applications working better with Windows Phone 8.1
You can download Live Lock Screen BETA in the Store here. Comments? How well/badly does it work on your own 8.1-powered device?