That's not quite true of Mystery snails. If it's female, it can lay a lot of eggs but they lay them above water only, so it's easy to remove the clutch if you don't want it to hatch. You can drown a clutch or crush it before you throw it in the trash or burn it.
Nerites, so far as I can learn, have sexes. so you only get eggs if you have females. But sexing them is impossible, unless you see one laying eggs, in which case you know it's female. So if you get Nerites, chances are you'll get eggs too. The eggs do fade away gradually but it takes a long time and meantime they lay more of them.
They are a tidal marine species, and the eggs are designed to stick around until conditions favourable to hatching occur. That's why they're a bit of pain to remove from wood. But I find a scraper or coarse scrubbie pretty much takes them off most things, if they bother you.
Mystery snails can be sexed, but usually you find out you have a female when you find a clutch of eggs above the water. If there is no surface they can lay eggs on, sometimes they fall out of tanks looking for a suitable place to put eggs, so covering the tank is not a bad idea. They will lay on the underside of hoods, or glass covers and on the side glass if there is enough space above water- they need at least an inch of bare glass and 2- 3 inches is better, assuming you want babies that is.
