Although it is less complex and less abv, it is a very good and cheap alternative for Green Chartreuse. With the low price (€14) point in the Netherlands, this is a very nice sub allowing me to make crushable GC cocktails like the Pina Verde without guilt.
Boomsma is sweeter and less complex than Chartreuse Verte. It is also considerably cheaper, not to mention easier to find. It won't replace the real thing for a neat sipper, but in mixed drinks it is a very good substitute, especially with a few dashes of Elexir Vegetal as mentioned above. I've made a few drinks that way with differences ranging from imperceptible to minimal.