What do you like best?
The fact that we can fill both display and mobile unsold inventory, both on Private Marketplace and Real Time Bidding. Also, the fact that there is transparency and control, for example if you need to identify an offending advert you can use their debugging tool as a Firefox add-on or ask to search through their creative database (Helix). You can also constantly update the list of blocked advertisers but also industry or category. Dashboard, reporting and presentation of data is also good, easy with vast capabilities, nice use of graphs. It is suitable for high volume of traffic which is international. Implementation is not complicated. Interface is straight forward (i.e. hamburger menu). You can also play around with the floor CPMs according to the specific market performance and you can pull your own tags so that you can set up deals at your discreption.
What do you dislike?
Support can be an issue at times when you need a quick action (even if they have a 24 hours support staff) or when you cannot identify an advert that is causing an issue to your pages. We use a lot their VIP support! Few times ads have been mis-categorized for some reasons.
They do not have a creative filter like Google Adx (with Adx you can even upload a screenshot of the ad to find it) and their Firefox plug-in is only useful if you have the offending or bad ad in front of you on the live page. When this happens you can flag the issue directly from the browser plug-in to their team which is nice and easy in terms of communication. However, chances to get the live advert on the page are not high if you run international inventory!
Recommendations to others considering the product
Try to combine Rubicon with other platforms which are suitable for your needs.
Try to push CPM up by having direct network to compete with RTB within Rubicon itself for example if your ad server is DFP which does dynamic allocation of different types of priority and networks.
What business problems are you solving with the product? What benefits have you realized?
Selling international "unsold" inventory in high volumes and keeping a good standard of advertisers and ultimately some publisher control.
At the same time, as a recommendation, it is always better to use more than one SSP.
Rubicon is ideal for a larger international publisher with millions of unique visitors per month. You can also set the direct network (better CPMs) to compete with the RBT itself to push CPM. DFPP algorithm with its dynamic allocation will help to increase eCPMs.