I can only say that the cartridge I got from them was better than the Qu-Bd cartridge by far.
Also, their fan for me rocks. It's incredibly responsive to sudden increased loads, and slows itself down. I accidently stuck a razor in mine today and it scarred the blade *but didn't break it.* By contrast, my solidoodle fan lost a wing when my finger touched it [granted, there is more rotational energy in a 40mm than a 30mm fan.]
I would second the ebay suggestion. If for some reason you really can't use ebay (filter for "items in north america" to pay a few bucks more and get it much quicker), then I could part with one of my spares...but I'd rather not. Note, my spares are as good as E3D's, which are better than Qu-Bds (I have two failed Qubds resistors
).
I would disagree with the idea that the cartridges are not good for 300C. I suspect they will last a very very long time at that temperature. The trick is making sure you are very good about taking the stress off the junction of the resistor and wire. You do *not* want that bending back and forth. I have mine secured with the good red insulation and further supported by some kapton tape to get it in a fixed position.