I've used the Lenspen lens cleaning device for years. It works just fine, if used properly.

Blow off the UV filter to remove loose material on it before using the Lenspen brush end. Eyeball the UV filter surface to make sure the brush removes material therefrom.

The brush may only loosen material. Blow off the UV filter surface again to remove this loosened material. More brushing and blowing may prove necessary.

Next, after rotating the cupped end in its cap, use the cupped end to polish the UV filter surface, in a circular motion from the filter center to its edge. You may have to repeat this polishing to get the filter surface clean.

Blowing one's breath on the filter surface will add a film of moisture to it, which helps the cleaning effect of the cupped end.

Be sure to rotate the cupped end in its cap now and then during the polishing, to refresh the carbon cleaning compound on the cupped end.

Notice my use of the term "UV filter." I leave this filter screwed on the end of the lens at all times. This filter protects the lens surface itself from damage, while it keeps filth off the lens surface. The UV filter minimizes the necessity of cleaning the lens surface.

Over time, however, the ambient air will reach the lens surface, and deposit a thin film of pollutants. Yet, typically, the lens surface does not have large particles of material on it, due to the UV filter keeping such material from it.

All the same, eyeball the lens surface for particles. Blow them off, and use the Lenspen brush end if necessary to remove them. Repeat the use of the Lenspen cupped end to polish the lens surface.

Note that when blowing one’s breath on the filter or lens surface, the breath may carry spit with it, and this spit may deposit on the surface. Woe to you if this happens because spit contains proteins that adhere to the surface as if bonded there. The Lenspen cannot fully remove this sticky blob. So take care to when blowing your breath to avoid its containing spit.

If spit should deposit on the filter or lens surface, then a lens cleaning fluid and a microfiber cloth will become necessary to remove this stubborn deposit.

Note that a light brushing with the microfiber cloth can also remove particles from the filter or lens surface.

One may substitute a little air blower for blowing one’s breath on the filter or lens surface. Giotto and others make these blowers, in two or three sizes.

A complete filter and lens cleaning kit, then, will contain the Lenspen, lens cleaning fluid, a microfiber cloth, and an air blower. Don’t leave home without this kit.

I break this maxim all the time, by carrying only the Lenspen when shooting locally. The Lenspen and my breath do the job most of the time.

If spit should deposit on the UV filter, then I remove it and shoot with the bare lens. Later, at home, I clean the UV filter surface and put the filter back on the lens.