I currently am running both pushing 250 watt Radiums. With the Blue wave 7 the ballast is a tank and I've been running it for a couple of years now with no problems. They are hard to get these days due to not being manufactured anymore. Because it is a dual ballast I don't think you can run just one bulb. When I've tried the ballast hummed like crazy. The bulb fired but because of the hum I didn't want to hurt anything.
The AM Cube I just got and put on my frag tank. So far so good. It looks well built, is small, and is well ventilated with a fan. They seem to be readily available also. I just picked up two brand new ones for $60 a piece from an online vendor. I've seen them selling for up to $120 - $130 each on some other vendors sites. Fires the Radium perfectly as it would the Phoenix as well.
I don't think you can go wrong either way. It seems that parts are readily available for both as well should one of them go down.
HTH