Not all digi ballasts are convertible. I have a Lumatek 600 and it is HPS only, would need a conversion bulb for MH.
The reason for my question is I have an opportunity to get a 1000w ballast and reflector for a good deal and I have read a lot of people like the flowering they get from MH, and others combine MH with HPS for best of both so-to-speak.
I thought wouldn't it be great if the opposite of the EYE hortilux existed with predominately MH spectrum with a second HPS filiment and that's where found the link to that lamp. But you are right, they are expensive but I did find one for only about $30 more than the 1000w EYE and I think I might try it out. I might run a standard MH one harvest and compare to the new bulb on the next while trying to keep everything else equal.