Quote from heech:
I've traded with both, and currently trade Rithmic. You are not completely correct.
ZenFire is based on Rithmic technology (licensing their software)... but the two companies host their servers (+ datafeeds) separately. I have not had any serious connectivity issues with Rithmic's servers or data feeds in more than a year, and I trade (automated) 6 days a week, 23 hours a day.
I did have an issue ONCE with their risk settings being down on Sunday of Easter Weekend. I was able to pick up a phone and talk to their live support (and executive team) within 30 minutes, and get everything resolved.