I've done well with them in the past (there was one particular merchant I was promoting who is no longer with the program) and am still with them, though on a smaller scale these days ...
Positive: Free datafeeds, prompt payment, good support
NegativeIf a merchant's funding runs out they go offline and your links stop working! However, you can configure an alternate destination for broken links (highly recommended!). Or just use merchants who are set up for autopay.