That's voodoo magic. That "double discone" isn't any sort of discone at all...shame on them. A discone has a disk, and a cone, and has no matching device of any kind so its power rating is virtually unlimited (1500W is a piece of cake).
What the data sheet shows isn't any sort of discone, but rather a skeleton profile vertical dipole, and has a "40 Watt" power limit (rating) due, I'm sure, to a matching device at its feedpoint (a discone doesn't need any) -- probably inductive loading to provide coverage down to "25 MHz," which is ridiculous for a discone unless the discone is as tall as a building and nearly as wide. A real discone actually covers about one decade bandwidth.
I wouldn't waste money on something like this.
WB2WIK/6