A small downside to the model I have is that the top is hard to clean inside due to the opening mechanism which goes across. But I guess it's well worth it, for the mechanism works great and makes it a lot safer than most mugs.
I asked Contigo about the cleaning issue. They wrote:
"Thank you for contacting Contigo® and we apologize for the difficulty you experienced with your product. We are working on a lid that comes apart for better cleaning.
I have included a tip that may be helpful. Sprinkle some baking soda in the upside down lid and then add an ounce of lemon juice. The chemical reaction sweetens the whole inside of the lid. Rinse the lid with hot water and let dry, the hot water will clear out anything the baking soda and lemon didn't reach."
By the way it foams, it looks like it's a pretty powerful cleaning process.
By the way, doesn't Blogger seem unreliable recently? I keep getting "service unavailable" error messages when loading a page.