We never had good lucky with Cyren, overall, I'd give it a 4/10. The stuff it did catch was stuff RBLs would have knocked down on their own, other stuff it would classify as spam that was not, then it would not catch blatant spam emails that RBLs were not yet identify the source as spam.
The same with Sniffer, many FP, didnt seem really any better or worse than using some of the higher quality RBL lists to score on source IPs. Sniffer I dont think really any any "intelligence" behind it, it appears. We also tried it directly integrated into our Postfix gateways just to see if maybe it was any better not attached to SM and the results were the same.
We have a customer who uses Cyren at the MX level, and Cyren processes all their mail directly, apparently it has more features than what the SM integration offers and that customer has told us they havent been very impressed over the last 2 years with them.
Maybe the announcement from Tim regarding Cyren brings some better news?