Has anyone ever used these ballasts? I don't believe that these are being banned, so they might be the only way to continue buying magnetic F40T12 ballasts. I would buy one and try it, but I can't drop $50 on a ballast that I don't really need!

If it is not affected by the ban, then  We'll have to wait and see. Fifty dollars is quite expensive, but then it is a "double" ballast as normally with T12, you would need two ballasts to operate four lamps.

Side note : Are you in Canada ? I am wondering how easy it is to order from 1000 bulbs. I am in Canada, and would like to order, but not if I need to pay brokerage fees to have an order cross the border. Thanks.

How hard is it to make your own by rewinding an existing transformer to match the values ?

"Magnetic" ballasts are about to be banned due to too low system efficacy (even 100% efficient, so no loss, ballast would fall short for the efficacy requirements, as the lamp itself have ~15..20% lower efficacy at low frequency compare to HF drive)

And for electronic ballasts if I remember well, there is a requirement, then when single lamp fail, the ballast can shut down maximum one other (so max two lamps are allowed to not operate as a result).
While EOL protectons usually shut down the whole inverter, that mean maximum two lamps per one inverter. As I doubt someone ever marketed ballasts with more then one inverter in each unit (two separate units would be for nearly the same cost, while they offer greater flexibility), either the ballast is not protected (and I'm not sure, if this is acceptable due to fire risks), or banned...

I'm not aware of any outright ban on magnetic ballasts that is coming here in the USA. There are higher efficiency standards that are pending, but I don't think that they will affect more ballasts than the last rulemaking in 2005. The 2005 law only affects one- and two-lamp ballasts, not four-lamp ballasts, so magnetic ballasts are still available in four-lamp configurations, no matter how inefficient. Other ballasts are exempt such as those for non-standard length tubes.