Don't get discouraged I Start out with about 2-3 lbs of lump & two splits then 1 split every 45 minor so to maintain temp and I cook at 300 95 % of the time. You can use charcoal but Splits are easier and more efficient and make better tasting BBQ. Most folks who complain about a CharGriller being a leaky fuel hungry beast of a cooker that won't maintain temp without constantly having to fiddle with it. I have $30.00 in materials to mod mine it runs even temps across the entire surface and eats 1 split every 45 min.
Offsets are all about a good flow from intake to exhaust, having the right sized fire box to support the cooker is critical. The one on a CG is 85 % the size it needs to be so it suffers if you stuff to much stuff into it. It also does not have enough draft under the fire to get a good burn in it's original configuration. The base of the fire needs to sit in the center of the intake so there is a place for the ash to go without smothering out the fire. This cooker requires a Small Clean & Hot fire.
If you go putting a Big Charcoal basket in it you block up the air flow around the fire reducing the draft. That leads to stale smoke and a smoldering fire and creosote deposits on your Brisket, Ribs Shoulders or whatever your cooking.
This is mine in action
Puffin Sweet Blue Baptizing the Brisket