I have a Razer Naga and I'm quite happy with it, and I just got my room mate a Naga Hex for Christmas. My other room mate also has a Razer mouse (the Tron one? Not really sure what it's called), I have the Blackwidow Ultimate, and we have 2 Nostromos, none of us have ever had a problem with any of Razer's products.
I don't think you have to use Synapse to use the mouse, but personally I like being able to easily configure and switch between multiple gaming profiles. As for monitoring your activities...I highly doubt it. You might want to read
this, it sounds like it's related to whatever you heard.