I wouldnt buy that gun.

To your question, a Charlin is not a Darne. When they have a safety lever, that safety has a very stout little leaf spring, that makes the safety a bear to get on and off. It sounds like a minor point, but, I got rid of my Charlins over that minor point. This one is missing its safety lever. Not good.
You may see some internet prattle about how superior a Charlin is to a Darne, how smooth and refined the action is, and whatnot. Is is BS, usually prattled by someone who has a Charlin to sell. The smoothness is only a factor when the gun is cocked, and you are cycling the action for fun. When it is time to cock either gun, they take the same amount of effort, and make the same amount of noise. There is an interrupter in the opening key of a Charlin that keeps the gun from firing if it isnt all the way closed. Good idea, but, the bolts that hold a Darne closed are already engaged before the gun can be fired. A Charlin has no bolts, it is purely an over-the-center device. If you use ammunition that is a bit too long in a short chamber Charlin, the gun will often reward you with torn off ends on the spent cases, savage recoil (same as any other light gun with the wrong ammunition) and an opening lever slightly out of battery. It cant open at the shot (over the center device) but, that fact alone doesnt keep guys from wetting themselves when they see it.
Use the right ammunition, and it isnt a thing.

They are similar, but, different designs, and one really has to discover which he prefers, by using both. Some guys love em, some guys (me) sold their Charlins and stuck with a Darne.

Best,
Ted