Another Great Weber Accessory
As I'm sure is the case with most people, I bought these for indirect cooking -- you have great control of placement of briquettes when you're doing indirect cooking. When you're doing a turkey, you want to pile in the coals but insure they stay to the sides. For this, they work great.

For me, the surprising part is what a great aid they are for direct cooking. By placing them next to each other, you can intensify the heat source and actually raise (as a result of stacking up the briquettes in these) the level of heat source closer to the grill. A great addition when you have something you want to sear at the start of the grilling process.

Indirect heat
These are used for holding the coals while a drip basket is positioned between them for indirect heat cooking. They work great, start the coals in a chimney or move these inward a little for air flow and use fluid. Chimney always preferred. Position drip tray after lit and roast away!

Good, but they ain't no chimney
These came with my 22 1/2" Performer grill. They work, and are better than just a charcoal pyramid, but they don't match a real chimney starter. If I had to buy these separately from the grill, I wouldn't and would just buy a chimney.