Since I am highly suggestible, I had to try these myself. The Baked guys have their own version, which differs in the shortbread section, but the myriad other recipes are largely the same. I went with a recipe from Joy of Baking.
They look good, right?
But honestly, I'm underwhelmed for two reasons: the shortbread layer is pretty bland and extremely crumbly, and the caramel layer isn't caramely enough. Oh, and it was a pain to cut - crumbs everywhere, and the chocolate layer cracked. If I had cut it last night when the chocolate was still a bit soft, I might have avoided the cracking, but then there'd've been crumbs stuck to the chocolate layer. A mess.
Back to the caramel... I was expecting a deeper, chewier caramel taste. Perhaps dulce de leche would have been a better choice? It certainly would have been faster! I used the microwave method to caramelize the condensed milk, because it claimed to take 15-20 minutes rather than 60-90, but it was at least a half-hour process. At that rate, I could have thrown it in a double boiler, which would have required little attention except the occasional stir. I got impatient, or I would have cooked it even longer - it was showing signs of becoming a nice golden color; perhaps that would have deepened the flavor.
I'll leave you to click on the link for the recipe I used, but because it's not one I'd make again, I'm going to be lazy and not post it myself. I think I'll go buy a Twix bar.