Looks like a good deal on the bulb!
I made Cylocommuter's Retinal Blasters: http://www.bikeforums.net/showthread.php?t=368772

I tried an led mr16 bulb (earlier and different version than yours) and it would fit in the base...but the bulb was different enough that the front ring would not fit.
At $15 I'd go ahead and give it a try though.
My bulb cost me a little over $40.