It's held once a month in a gorgeous converted canal house with three floors (salsa/bachata/R&B) and is always well attended. In the salsa room, expect a fair amount of romantica from DJ Ryad, but there's usually another DJ so you also get plenty of harder stuff. The crowd is a mix of on1 and on2 with varying levels from beginners to pros. To me one big negative of this venue is the uneven floor. I find it very hard to stay on a straight slot and it's tiring and more collision-prone. If it hadn't been for that, I'd go more often.
Are you going tonight? The Salsa Beach Festival is also on in Den Haag, I don't know if that will affect the attendance.
Apparently MonteCristo is ditching salsa, and the Extremos salsa school is moving to a new venue on Jan van Galenstraat from November. It's a bit of a walk (about half an hour from the centre) but there are buses from the Centraal station.