I think it's a bit of a gimmick for more than searing - and I won't say that it's worked all that well for me in the past for that either.

But I wouldn't let lack of direct heat keep you from getting a pellet grill if you're worried about grilling burgers. Just pump the temps up to 400-500 degrees and use the entire surface to cook your burgers. I've had no complaints when I've done that - and it's nice that you don't have to worry about grease dropping into the flame and creating problem stops that burn your burgers.