As a rule, customers will balk at buying a digital title that's worth as much or more than the print version of the same title. Some publishers have a standard policy of selling the digital title for half the cover price of a retail print copy, while others charge a little more or a little less. The simple fact, though, is that a digital title has as much "value" for its reader as the physical copy, particularly when you're talking about the ability to access the title readily via laptops or mobile devices at the gaming table.
Whatever you decide, we suggest you do not give the digital title away for free unless you're doing so decisively as a sales or marketing tactic. If you give your title away for free as anything other than a short-term special deal, not only do you perpetuate a misapprehension about the value of digital media in general, but you risk establishing a low-value perception in the minds of potential future consumers about the worth of your paid products.
That said, you might consider giving something like a minimal "starter" title away for free. This way, you get your brand in front of people and give them a taste of what's to come, but you don't give them everything in your catalog for free.