Question MH conversion bulb running on a HPS

Saw one of these for sale and started thinking about instead of spending money on a switchable ballast, using one of these conversion bulbs instead for when I need MH for vegging.

Has anyone ever used one of these?

http://cgi.ebay.com/600-w-watt-hydroponics-grow-light-HPS-to-Metal-Halide_W0QQitemZ260131015685QQihZ016QQcategoryZ42225QQcmdZViewItem

I do it I run an HPS on a MH ballast, I ordered from Metal Halide Light Bulbs, Light Fixtures & Tennis Court Lighting - Businesslights.com and loved the price and service, I payed 40.00 for a 120$ bulb

if you only have a 600w ballast, this would be the way to go. if you're still in the market for a ballast, you may want to check out the ceramic metal halide lamps by phillips. Phlips MasterColor Ceramic Metal Halide ~ CMH ~ HPS-Retro White the largest they make at present is a 400w. they run on hps ballasts and they are the only bulb you'll ever need.