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.