I've worked at both. My memories of CodeFlow are a bit faded but I don't remember it doing anything that Critique doesn't. Critique has the advantage that it's hosted on the web, while CodeFlow was a janky Win32 application.

I worked at both, but I left MS before CodeFlow was created. An earlier version of what is now Critique (called Mondrian) was already in use at Google when I joined, and predated me by several years. There might have been something similar before it, I don't know.

I have worked for both and prefer CodeFlow, my more detailed comment is above.