This is the first downloadable synth I ever bought online. After using the free mda-Version for quite some time I decided that as little as $19 should be money well spent for the GUI alone. And I did not regret it.
The shiny new interface is clean, easy to read, easy to understand and for a VSTi even relatively pretty. So this alone would justify the price.
But it doesn stop there. Imageline also added a second modulator which gives a lot more options for creating diverse and exprimental sounds. The effects and the excellent EQ add even more value to the package and especially the reverb is quite useful for creating spacey fx sounds. The delay is more of a "spice up" effect than a real delay given the reduced parameter set, it this respect it's highly useful though.
The only feature I really miss - and it's a quite simple one, too - is the ability to reduce the polyphony. Since the synth lends itself so well to programming bass sounds it would be nice to switch it into mono mode.
The DX is rather easy on the CPU, even with the FX turned on, and it didn't crash once so far in Cubse SX.
This versatile little synth has become an indispensable tool and ends up in almost every track I produce. I figure it's also a good starting point for those who want to try their hands at FM synthesis but are overwhelmed by the FM7 interface. With the nice GUI, the added effects and at this ridiculously low price you can't go wrong.