I've got one, and yes, they have been discontinued for more powerful models at an even smaller size.
The hum...I read about it and bought one anyway. When I first plugged it in, I could hear the hum. but only because I was listening to it and really paying attention to it. After 30 seconds, I didn't notice it anymore.
I have played several hours in live situations with the Superfly, and you will not hear any hum whatsoever onstage....too much other "noise" going on. Drummer banging on something, guitarist tuning, keyboardist doing something...never a dull moment.
The "hum" is a non-issue, IMHO. Don't fret it. I have a Peavey Max 700 whose fan is louder than the Superfly hum. Seriously.