I just installed a demo of Lock & Load hoping it would actually work vs. SmoothCam built into FCP. Since upgrading to FCS 3, I have had some serious problems with the SmoothCam filter - the bottom line of which makes it unusable. Using Motion doesn't work well either because then the clips in the timeline are shortened, making for a lot of clean up.
With Lock & Load, motion tracking was completed in only a few minutes for my whole timeline, vs. several hours with SmoothCam. In my timeline, I have a lot of clips that are all from a full-tape capture. Lock & Load is intelligent enough to know that I have in and out points for my clips and uses that to evaluate from. SmoothCam wants to evaluate the entire tape, resulting in hugely long evaluation times for motion tracking.
The controls are just as simple and you get a few more options in L&L that are absent in SmoothCam: Lock Down, Direction tweaks, Zoom mode, Max Margin and Max Zoom Speed. For my footage, I set the Max Margin to 3 rather than the default setting of 5 it went to. This has resulted in incredibly smooth footage with a minimum of final cropping needed to hide the moves. With Zoom Mode, Smart Zoom (as the default setting) seems pretty smart, though I can think of a reason or two to change it to Fixed Zoom. All of the other default settings seem pretty effective - at least for my current footage.
The final render & export will shortly follow. I'd be happy to show a before and after comparison on my ScreenCast page if anyone wants to have a look.