Always monitor the meat temp. While 140 is a little low for me, I like mine about 145. (yes, those few degrees really do mean something). He is right about only 30 minutes smoke at max. Maybe even 15 to 20 would do. And monitor internal temp!!!! That is so important. Keep initial temp between 180 and 220 for the smoking at the max. Pull meat when it heats 145 and let rest. It should hit about 155 after a few minutes. We wrap ours in foil for a few seconds and let rest so it reabsorbs the moisture.
And a not a bad thing to put a pan of water while you are smoking so as not to dry the meat out.
You should only salt and pepper them. No need for anything else. We cook grass fed beef all the time. It is actually a bit fattier if they prep it right.
Then put a near 30 second sear or so on both sides of the meat. No need to burn it. Causes carcinogens. BTW, putting rosemary on it while grilling cuts down on carcinogens by about 80% or more.
When cooking meat to different temps what you are doing is causing different levels of drying of meat, which means loss of moisture. That is why low and slow means something, still not bad to keep it moist.
By cooking to 180 for two hours you dried out the surface towards the heat and caused it to form carcinogens. That is also why you flip them, to prevent moisture loss from each surface. It forms a crust to prevent other loss of moisture in the rest of the meat, but it still does.
Almost all professional bbq people keep meat moist also by adding moisture to the cooking area. It also helps keep max heat at 212 degrees because of the conversion of water to steam enthalpy. Change of phase and all. This is why pros all show putting a pan of water somewhere in the cooking area when cooking low and slow.
For great hamburgers you would like a nice juicy moist hamburger with a nice surface finish and a bit of smoke. With really good meat, like grass fed, you do not want to hide flavor with anything else. That is why establishments put spices and juices on their cuts, to hide the cheaper cut of meats and the flavor.
It is again, simple. Set smoker to smoke, monitor internal temp of meat (140-145), pull when hit that temp, give it a very quick sear, rotating 90 degrees once, and then flipping. Probably no more than 30 to 60 seconds per side.
Frozen is a little different, but I would let thaw before hand. Season with salt and pepper and put in refrigerator for hour or two.