I have both the LMP and the Mobee...
...and I see use for both of them.
I have also done extensive work on Sophisticated Circuits keypads (an elegant little thing that is, alas, no longer available) as well as with other cheaper USB models and one Microsoft BT model (which didn't work worth a damn with the Apple OS X).
If I'm in heavy number mode (spreadsheet entries), I go with the LMP. The key feel is slightly different, but it works well, the angle is similar, and the thing doesn't slide around like others that I have used over the years.
HOWEVER...
One thing that you cannot do with the LMP is to program one of the keys to act as a standard "Delete" key. There is a "Forward Delete", but I prefer to go at it from the other direction, particularly when updating the prices on Amazon.com books that I sell.
As a result, editing involves moving from computer track pad to computer Delete key, and then over to the number pad for the numeric entry. Cumbersome at best.
The function keys do work, but there's nothing that I can put in a function key without some way of picking from a menu.
The Mobee is a different item. It offers no tactile feedback (vital for quick accurate number entry by touch) and only a scarcely audible click from the computer. The film adheres perfectly to the track pad, and gives me three different optional layouts (I choose NUM20). It too has the row of function keys across the top, the page up and down keys, plus two completely programmable keys off to the left.
Once the software is installed on your computer, you just activate the numeric mode, then program the keys as you desire. (The largest layout offers a whopping seven programmable keys.
Another feature is that it can be programmed so as to only accept a light touch, only to accept a touch heavy enough to "click" the trackpad, or for both.
I use the LMP for the serious number entry, and the Mobee for the editing functions that it possesses. (It also has arrow keys for moving around within a document, as well as page up and page down, home and end.) Plus, if you have the Trackpad already, it's twenty bucks cheaper, as well as retaining trackpad functionality. And, one less thing to carry.
As for those who have commented that we don't need them in the first place, they obviously have never suffered through a large spreadsheet with data entered into a thousand or so cells. While I can touch type at about 40 wpm, my accuracy with the numeric row is way too low to trust figures that have monetary implications with touch typing upon it. For that sort of stuff, a numeric keypad is the only way to go.