The LensPen has been around for a long time, but I have only been using them for a short while. I got tired of chasing oily marks around my lenses/filters with microfiber cloths and Pec Pads, and decided to give a LensPen a try. And I am glad I did - it lifts these marks right off.
When cleaning a lens, I always use an air blower first. If necessary, I'll next use the retractable lens brush included with the Lenspen to remove any remaining particles that could scratch the lens. If the lens is still not clean, I will likely use a Pec Pac / microfiber cloth method next. But, the LensPen is really good at removing the hard-to-get-off marks such as oily fingerprints without making a smeary mess.
The Lenspen uses a "special non-liquid cleaning element, designed to never dry out" to lift dirt from optics including camera lenses, binoculars, telescopes ... The LensPen, sold under many different brand names, is cheap and travels very well. It makes a great addition to your cleaning kit.