I have a pair of Fiskars scissors that is a corner rounder. I've had it for years, and I use it all the time. I haven't seen them in any stores, so I don't know if they even still make them. I also have some corner rounder punches that I use. I know a lot of people who use the CM punch.
I have a CM corner rounder and a SU corner rounder. I know that Ek Success also makes corner rounders. You can find them in Michael's, Joann's AC Moore and other craft stores. I know that sb.com also sells the Paper Shaper corner roundser in small medium and large punches.
I actually do not like the Creative Memories corner rounder. I find it is too difficult to use.
I prefer the Ek Success Paper Shapers Corner Rounders. For marge projects, multiple sheets of paper, or chipboard I like the Zutter Round It Alls.
You can remove the guide on the Paper Shapers ones and use them to make a scalloped border along the edge of something too which is a feature I really like. Stampin Up sells their own smaller version of this corner rounder. It is very easy to use.