Does just what it’s intended to. By using the lid, I can extend a single charge on my Ember to well over an hour, the time it takes to get through the entire morning paper, and then some, while sitting outside. Great addition!
The sliding lid is well made, a simple design that's easy to take apart for cleaning. I appreciate that several extra sliders are included in the purchase.
10/10. I suggested this product to the Ember team a while back before it existed, and I am happy that they are listening to their customers (I'm obviously not the only one). My dog loves to get into my coffee while I'm not looking and this has changed that 100%. She cannot get into it at all, even with the slider open. The lid fits super snug into the mug for a spill-free fit. Even when I accidentally over-pour my coffee, then put the lid on, the overflowed coffee will rise out from the top of the opening, not down the sides, keeping it clean and tidy even when I'm not. :)