One of the things I grabbed from the big Fing'rs display that was at WalMart a while back was the Get Spotted topcoat kit, which has a full size (.45 fl. oz.) bottle of black spotted effect polish and two mini bottles of regular polish in hot pink and blue.
The side of the box has the simple instructions (and here you get a peek at the state of my hand during swatching sessions, with four bare nails and a thumb with whatever mani I was wearing last): let base color dry completely, apply the spotted topper, let dry then add clear topcoat.
The directions say to use a thick coat of Get Spoted for "less and larger" spots or a thin coat for "more smaller" spots. In the swatch below, I went thick on my index finger (top) and tried to go thinner as I moved toward my pinky. It made a difference, but not much of one. I never managed to get a truly thin coat or all that many spots. (The base color here is Sally Hansen Hide 'n' Pink topped with Costume Jewelry.)
You know I had to do a comparison, so I rounded up OPI Black Spotted (which I don't believe I've used since last year) and Layla Bubbly Effect Black Forest (which I got thanks to Sparkled Beauty, who grabbed me some in Canada; this line never made it to my Ulta here in the states and Ulta's the only place I've ever seen Layla to buy in person).
Left to right below (over Sally Hansen Guess Blue): OPI (thick coat), Fing'rs, OPI (thinner coat), Layla. I think the Layla wins this comparison, though perhaps if I thinned the OPI and Fing'rs they'd do better. As you can see, none of them are especially easy to clean up.
I wasn't too happy with how the Fing'rs behaved up to this point, so I gave it another chance, with one finger of OPI Spotted for comparison's sake. Left to right below: 3 fingers of the Fing'rs with OPI on my pinky. The OPI is easier to work with. (Base color is Sally Hansen M-asked to Dance topped with Myst-ique Pink.)
Of these three, the Layla is my favorite. The Fing'rs was definitely the most affordable, though, and who knows maybe I'll like it better if I try thinning it. But as long as I've got the Layla I don't have to mess with that.