The biggest difference between the Lottie London Wing Edition Stamp Liner Duo ($7) and the other two stamps I tried is the price. The chunky pen comes with a stamp on one end and a liquid liner on the other, similar to the Lyda Beauty pen.
The stamp itself is thin and straight with no curve to it, so you get a razor-sharp wing when you apply it. It goes on ultrapigmented with no need to fill it in and has a flat, matte finish.
Image Source: POPSUGAR Photography / Jessica Harrington