There are so many affiliate networks out there, so it's a lot easier to just join one that has it all. In fact, they often have higher payouts than working directly with the advertise (because they are working with so many partners, they have a lot of traffic, so in the end it benefits you). I worked for a larger publishers so I had a great account manager who was responsive, but I'm not sure how it would work for smaller publishers.
Another thing I'd like to add: if you are a smaller publisher, this is a great network to join. Smaller publishers might have trouble hitting threshold on multiple networks, so when you have all of your traffic in one place, it's much easier to hit the minimum.
What do you dislike?
It's still great to have those direct relationships on your own. You can get the latest updates and have more room for customization.
The deep linking is great but doesn't work for everything. I would also consider it confusing if you were new to the affiliate world.
Lastly, the images sometimes aren't updated for a bit. That could be updated more frequently.
What business problems are you solving with the product? What benefits have you realized?
It's a great way to monetize your blog or website. They have so many different brands available.
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