The Traeger pellet grill/smoker is best described as a wood fired convection oven. Although it can be used for grilling, your gas grill is far better at that task as it heats up quickly to a high temperature. Although it does provide smoke flavor to the food, it will not provide the same level of smoke as a stick fired offset smoker.
Where the Traeger excels is in longer cooks. You can fill the hopper with pellets late in the evening and let it run unattended all night long. You cannot do that with an offset smoker.
The Traeger does not quite get hot enough to properly sear steaks or burgers, although it can be used to cook both. Some people purchase GrillGrates to provide enhanced searing, but I did not find them to be all that helpful.
I solved that problem by purchasing a gas-fired griddle. I will smoke my steaks on the Traeger at about 225F until the internal temp reaches about 120F. Then I will fire up the griddle on high and sear the steaks until they finish at my desired internal temp, which for me is 140F (medium), but might be different for you. That way I get the best of both types of cooking.
As for burgers, while I did cook them on the Traeger before purchasing the griddle, I now saute onions, sear my burgers, and toast my Brioche buns slathered in mayonnaise on the griddle.
The Traeger is great for cooking chicken, pork, larger cuts of beef, and cedar plank salmon. It can even be used to bake a pie or a pizza..
One word of advice: DO NOT TRUST the Traeger temperature readout. Get a 3rd party analog or digital thermometer to check the cook temperature. Adjust the controller to give the cook temperature you want on the 3rd party thermometer.
This can avoid a lot of frustration.