A good cocktail, but not a notably better than a more traditional espresso martini, or the Black Espresso (recipe on the website). If you are looking for a rum/espresso/PX recipe to try - try the Black Espresso first.
Used Havana Club 7 yo and Borghetti. The only perceived fault I can suggest is the roasty and nutty nuances of the espresso are ever so slightly muted. It's got a surprising degree of dryness to it, or maybe I diluted it a touch too much. At any rate, it's a marginally more interesting Espresso Martini, but not exactly preferable to one.