I will keep it short.
Razor uses additive synthesis using 'partials' and can be used with Reaktor or Reaktor player. It features UI that is friendlier than most of the synths on the market. In one word, Razor is special.
Razor is one of my favourite synths for many reasons but I feel it's my duty to warn people that it may not be what they are looking for. It is special in the way that it can create sounds that you really cannot achieve with other synths; the downside is that whether those sounds are actually usable is another story.
It isn't certainly synth that does everything; at what it does, it isn't even close to being perfect. You may end up noting that sonic characteristics of presets can be harsh and dull and anything in between. To our rescue, there is spectral clip and safe bass setting which adds or subtracts bass and top frequencies respectively. I have to say without these two features the synth would be very much out of control.
However, with filters it features with modulation options and 'sidechain' modulation which lets you modulate more than one knob at a time, this isn't certainly a synth that goes for instant usability. It needs careful tweaking, and even then you may need help from aforementioned two features to control your sound.
Many synths use word 'innovative' and so does Razor, but I feel it is one of very few synths that actually deserve this title. As I said, it does not do everything; it doesn't try. At what it does, it can fail. But the point of Razor is that it can really make some otherwordly sound.
So if you are looking for another subtractive synthesizer or VA, this is certainly not the place. But if you are looking to add to your sonic arsenal, you will find that Razor can offer you sound that you've never dreamed of. And certainly spectral clip and safe bass settings make it much more usable. It could certainly be my sound design ability, but you may find that sometimes it can be difficult to get the settings right, for it demands near exact settings for a usable patch. But if you love playing in your sonic lab, tweaking settings, coming across failures, willing to try an additive synthesizer, or experiencing sound that you would have not even dreamed of, Razor is for you.
I don't like giving out numbers but for sound I would say Razor is at about 7 or 8. But for its innovation and how tempting it is to get this unique synth at such agreeable price, I will give it a 9.