Cast iron grates can work, but GrillGrates are better for grill marks. If you would rather sear, then a cast iron skillet or flat griddle would work.
Grill Grates are easy to use. Get them hot and put the food on them :-D Just like everything, there are some tricks. I prefer to have them at 600 degrees for SCA steaks (an IR thermometer is a great tool). That gives me good grill marks and still gets some color on the rest of the steak. Too hot and the marks can get scorched and the rest of the steak will be gray. At 600 degrees my cook time is approx. 6 minutes (90 seconds, rotate, 90 seconds, flip, 90 seconds, rotate and 90 more seconds. unless the steak is thin, or at one comp, at a higher temperature to start due to excessive heat, that usually gets to to around 120 internal. Then I move it to indirect and cook to my desired internal temp for medium.