Yesterday though, I bought a Barry M Croc Effects one just to try, and I love it! I think it's because it's that bit neater and more even than the crackles.
Here it is over Barry M Tangerine, a nice shimmery bright orange.
With Croc Effects you have to apply it when your base colour is still a little damp. If you apply it over very dry polish, nothing much happens. The croc effect takes quite a while to appear - the bottle says 3 minutes, but depending on how thickly it's applied, it can take up to 5 minutes.
You can see that my little finger looks a bit different to the others - I applied the croc effects on that one a bit more thickly, and it has cracked differently to the other nails. It also took a lot longer for the effect to develop. For the other nails, I managed to apply the polish a lot more thinly, and I think it made a better effect in the end. Not only is the croc effect more pronounced, but I prefer the colour as it's not so intensely black, and seems a little more browny.
The application was nice and easy once I'd got the hang of it - the first few nails I did, I put it on far too thickly, or over too-dry polish, and nothing happened, but after that it was pretty straightforward. This was £3.99 from Superdrug, but I've also seen it in Boots.
I am planning to try it out over a gold foil next, and also over something like a nice bright pink. I still don't like crackles, but I am definitely a convert to croc effects!