I made and installed a grill block last month. First created a cardboard cutout that fit the grill. Then traced the pattern onto Lexan and cut it out. I cut and oval around the front emblem since that part sticks out from the rest of the grill. Plus between the Toyota "T" emblem, it's open so a bit of air can get through. I drilled pairs of holes and zip tied the block to the grill. So it can be removed with a knife if needed. The lower grill is also blocked with 3 zip ties. The two triangles on either side are not open, just aesthetic.
So far, it's hard to tell what type of aero or efficiency affect it may have but I'm sure it can't hurt. My daily commute is only 8-9 miles each way so the engine barely warms up, but it's quicker now with the grill block.