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*Floater*:I don't see any 21W HID's mentioned on OMS' site: http://www.omsdive.com/lights.html
Maybe an older, discontinued model?
Anyway, just double-check that it's a 21W HID and not 10W. Also, how long is the burn time? Battery type? Bulb type (WA or BS)? Adjustable or fixed focus? How old is it? How many dives on it? Any problems in the past?