The length of your headline and your copy will depend on whatever works for whatever you are selling.
And the only way to know what works is to test different approaches. Test various headlines to see which works best at capturing attention and communicating a benefit. Test the amount of information you provide. Does more or less work better at producing the desired action?
Ultimately, that’s the only answer that will ever matter to you.
The important word in there is “test.” It seems to me that, online and offline, we have forgotten the benefits of testing copy, themes, product placements and making modifications based upon the results. In this always on world, I’ve seen a lot of people just push forward with one decision and never take a step back to see if they’re going in the right direction.
And I’ll admit, I’ve been guilty of this on more than one occasion myself. Let’s all strive do to better.