Thanks Chuck, I picked up 2. Shipping was $10. I know they're on the heavy side, but they should work just fine in my SBR.
If the drum isn't your style, the factory Glock happy sticks are $28.99 each at Brownell's right now:
https://www.brownells.com/magazines/handgun-magazines/magazines/magazine-fits-17-34-9mm-33-round-sku100002771-71433-49272.aspxNot a
great price, but not a bad one, either.