Most of us just use a sheet of aluminum foil on the lower grate when we want to do indirect cooks on the KK. As @tekobo said, almost no one here (save a few diehards) use the supplied heat deflector stone (not to be confused with the pizza stone - different material) - not even Dennis uses it. A simple aluminum pan works, too, if you want to catch the drippings or get the double-walled pan from Dennis if you think you'd like to roast veggies using the drippings.
I have no issues doing reverse searing on my 23". The basket splitter creates enough separation between the "hot" side and "cool" side. The only issue is cooking area. If you want to do a lot of steaks (more than 4 ribeyes/NY strips) at once, you might run out of real estate (assuming you're using the basket splitter). You can do a lot of steaks if you don't use the basket splitter and just use the main and lower grates - roast the steaks on the main at lower temps, pull the main grate out when they're almost done to final temp to rest, crank up the grill temps and used the lower grate to reverse sear.
That's my opinion. I've never owned one but have cooked on them at other folk's places. Plus, one of my biggest gripes about BGE is that this is considered an "essential" accessory, but you have to buy it separately - price gouging IMHO. Dennis doesn't do that - every accessory is a true add-on, nothing essential for doing basic cooking on a KK!