I just ordered mine (https://chassisengineering.com/shopD...ProductId=1545 ) I have been concerned with the structural integrety on my car since I cut off the old roof and welded another one on. They were $99.50 with free shipping.
They tie the front and rear frame rails together to increase the strength and decrease the flex, twist, and deflection of the unibody design. Crawl under your car and you'll notice there's no "frame" in the middle. The only thing holding it together is the floor tying into the rocker panels.
Those are the same ones I got about a year ago. There well made with pretty thick square tubing, and they lined up perfect on my car.