Going by the pictures on Quirky's website, a "stem" with a serrated edge is pushed or twisted into the fruit and then a pump attachment works to pull the juice from the inside. In theory, this sounds super-nifty. It would be a very practical way to add a bit of lemon (or other citrus) flavor to your dish without the hassle of finding a knife, squeezing the citrus, and picking out the seeds.
But I have some conceptual problems with that design. Would the bit of citrus skin punctured by the stem end up blocking the flow of juice? Since citrus is segmented, do you have to constantly move the gadget around to another location? Does the pump create enough pressure to burst apart the little balloons of citrus juice in each segment? Do you get all the juice out of the lemon? Does the two-part gadget hold up over time?
I think this is one that I'd need to see in action before believing. The Stem isn't in stores yet, but according to Quirky's website, it's on the way.
Related: Top 10 Most Useful Kitchen Gadgets