Hope you get to see this, as it's been a while since you posted..anyway..
I got the full version of this synth and have to say it sounds pretty good, though it does feel a little "dated" to use..just a UI thing really. I think it's really a case of trying the free version to see what you think of it yourself.
For the record, I use this synth a good bit and think the sounds it makes are really good, but I've found this is the kind of synth that requires you to play around with the on-board FX on each sound to really bring out their best. Some of the strings sound really cheap out of the box, like what you'd expect to find in a free VST offering..but like I said..play with the FX, such as reverb..and they really come to life and sound pretty damn good.
In short, if you're the kind of person who likes tinkering with your synth, then this is right up your street..but if you're the kind of person who prefers to just open up a preset and play out of the box, then you might want to try something else..but still, give the free version a go first and see for yourself.
..also, I should add, on their main (IK Multimedia) site there doesn't appear to be a link ofr it and a search shows no returns either..as well as no sign of it under their "free" link on the site. My guess is they don't offer it anymore or there's an issue with their Soniksynth site.
Don't know what to suggest really, other than keep trying..as well as try looking for it on computer mag sites that give away software each month. Granted, you might have to take out a subscription or buy a copy of a mag for the month in question, but if you REALLY want to get a copy of this synth then it might be worth it to you.