I have a full width set for my CS450 and I'm really happy with them overall. Most of the time I leave only 1/2 of them in (on the left, over the firebox), and have a regular grill on the right half. This makes things pretty versatile for the amount I typically smoke and grill.
They have also replaced my use of baskets for things such as fajitas - I put the grates in full-width and upside down as a flat-top. They work really well for this, and cook much faster and more even.
The CS450 has a searing port, but it tends to have a lot of flare up with regular grates - the grillgrates help a bunch with that, though it can be tricky to keep them below 800 degrees when over direct flame.