mda's DX10 is a simple 2-operator FM synth (3-op if you use the special FL Studio version). It has no GUI, instead you are presented with 16 parameters in your host's default interface.
A lot of people seem to compare it to Yamaha's classic FM synths, but let me tell you: it's not comparable. It cannot even be compared to a Yamaha 2-op, such as the OPL sound chip. Where Yamaha-style FM is more warm and punchy, DX10 is more metallic and acid-like. Everything seems to sound like that UK "Donk" bass sound as you crank up the modulation amount. Also, its envelopes are rather limited. Instead of ADSR, it uses a sort of strange ADR/DSR envelope. In comparison, the OPL2/3 used ADSR, the DX21 used a ADDSR, where a secondary decay rate is applied to the sustain, and in the DX7, a freeform 5-point envelope is used.
Suffice to say, you cannot model 2-op Yamaha sounds accurately using DX10 (without losing your mind that is), you can however use it for its own merits. One of those merits include a waveform modulator, where you can modulate between a sine and "saw" approximation that contains additional harmonies added to the fundamental sine.
It can definitely sound interesting in its own right if you play to its strengths, but don't be fooled, it's not a Yamaha clone, and you will be hard pressed to make any decent brass sounds.
For more information about this plugin, here is below in italics a short extract of the description from the original page (before he's gone to Sourceforge where he has upgraded all his old plugins, then ported them to 64-bits... and added some new plugins that are not yet in the KVR Database):
"Sounds similar to the later Yamaha DX synths including the heavy bass but with a warmer, cleaner tone."