I run a small health and fitness business on the side and Bing has been one of our most productive sources of traffic. The conversion rates are much higher and as a result, the CPA (Cost Per Acquistion) is lower than Google Adwords on Facebook. The only issue is the low volume.
My friends Perry Belcher and Ryan Deiss at Digital Marketer have also had the same experience. They operate in 23 markets (everything ranging from forex to water filters to survival kits) and their Bing campaigns are much more profitable.
You need to invest a little effort upfront in keyword research but once this is done you can almost do a set it and forget it campaign. Unlike Facebook where you have to worry about audience fatigue, on Bing it is net new searchers.
The other good thing about Bing is the excellent customer service. You can actually call and talk to a human. They may not always be super knowledgeable but there is clear intent to be helpful. Good luck being treated like a human by Google if you are not spending at least $10,000/month!