I've used Rain Legs for commuting for the past 5 years. They work great for that, but my commute is only about 30 minutes. If I'm out for much longer than that in heavy rain, I'll start to feel wet. (I too have only used them with fenders.)

Probably the biggest annoyance with them is having a wet butt. You pull up to a red light and stand over your bike, allowing your saddle to get rained on. The light turns green, you put your butt back on the saddle, and now you're wet.

They don't add any notable warmth, so they're great for those days when you look out the window and it is gray and looks like there's a light drizzle but you might have time to make it across town before it really starts dumping. In those sorts of conditions I never want to preemptively wear full rain pants because of the heat. Throwing on the Rain Legs has basically zero cost, so I'll do it anytime it looks like it might rain.

When packing for a tour I feel better knowing I can stay out all day in the rain if I have to, so I'll pack full rain pants.

I came across Taiga Velo Crocs recently. They're rain pants with integrated spats. I'm intrigued. I may try these next time I need to replace my rain pants.