Royal Oak 100% Charcoal - 1 lb.

Authentic charcoal grill flavor on an electric smoker? Possibly...
This pellet is without a doubt, the closest thing you'll get to traditional charcoal grill flavor from a pellet on a small cooker like the Ninja Woodfire or other electric smoker.

Charcoal (though also made of wood) is a cleaner burning fuel than raw wood and will produce less smoke than a plain wood pellet. Making charcoal pellets a SUPERB option for those with an aversion to a heavy smoke presence.

The skull's experience:
While I agree with everything above - becuase I wrote it ; ) I do feel the need to help manage expectations. These pellets, by their merit alone, aren't going to produce the EXACT same flavor experience you get from a real charcoal grill, It's similar, absolutely, but not exactly the same. not by  a LONG shot.

There are two key (but too often overlooked) contributors to what people associate with charcoal grill flavor:

One is the "fat smoke" that comes from the juices from the food dripping down onto the coals. That doesnt happen in an indirect, electric smokers. 
The second is the "Maillard reaction" which doesn't happen at the temperatures at which most people "smoke" food. Most smoking is done between about 220º-275ºF.  The Maillard reaction starts to happen around 280ºF.