I love going back to old synth plugins just to see what can be done with them. Neon is apparently the oldest VST instrument there is (came with Cubase 3.7 in July 1999), so that's right up my alley. I've given it a go, made a handful of tracks and sounds with it, and here are my thoughts.
Pros: The 3 waveforms (tri, saw, sq) ... they could have just made it a plain square. Being the first. Woodgrain panel.
Cons: Only 5-note polyphony (even though it's supposed to be 16). Oscillators waveforms are low quality and sound like they have a permanent low-pass filter. Filter lacks an "Envelope Amount" control. No individual waveforms for oscillators, or Osc volume mixing control. Osc2 detune only goes 7 semitones back and forth, so no octave higher/lower possible. ADSR envelopes are a bit clicky even when turned all the way off LFO depth (mod wheel) is weak, as well as the pitch bend range is weak.
In summary: It's not good at all. And being old isn't an excuse. Both Model-E (Steinberg) and Pro-Five (Native Instruments) were created before Feb 2000. That's less than a year later. Then Native Instruments came out with FM7 in Feb 2001, which to this day is one of the best FM synth plugins ever made. And Neon could have been better.
It's oscillators are pretty bad. Neon is advertised as having two oscillators, but the only thing you can do is detune Osc2 up or down 7 semitones, not even a full octave... There is no oscillator mixer or individual waveform selection. And that's fine, the real crime here is how horrible the oscillators sound. Look at the output through any analyzer and you'll wonder what happened to the high end. The high frequencies are all filtered out, so instead of rich harmonic square or saw waves, you get these bland waveforms. And they get worse the lower you go. It's almost like they're using a single-cycle .wav file for each oscillator!
The filter is also pretty bad. It's weak and you can barely hear the effect of turning the cutoff down or resonance up. And the filter envelope is hard-coded to react to the "sustain" level as the amount, no "amount" knob to speak of.
Even heavy EQing can hardly save this synth. Give it a shot, and see for yourself. Steinberg still offers it as a free download. It can make borderline acceptable basic sounds thanks to the ADSR envelopes, but even the waveforms of the NES sound better than these do.
Some great memories of this synth so it has a nostalgia factor... But most of all I seem to remember thinking "DAMNIT, FILTER, OPEN!" because it seemed to be impossible to get the cutoff to go very high at all.
In the manual it states "The Neon is polyphonic with up to 16 voices. However, since each added voice consumes CPU power, the maximum polyphony may be limited by the speed of your computer."
However I can only get 5 voices out of it. Is it inaccurately determining modern CPU speeds or did they outright lie all these years? Oh well, it's a piece of crap anyway. The CS40 actually has 8 voices but it's advertised as "polyphonic with up to 6 voices". Nothing but lies.