The LCA brackets lower the attachment point of the LCA to the axle assembly. That insures that even when the suspension "squats" on launch, the axle end of the LCA will stay below the body end of the LCA. That insures that the LCA is "lifting" the chassis, and the corresponding reaction at the axle end it to force the axle down toward the pavement - increased traction. If you get it the other way, once the axle end is above the body end of the LCA, the LCA forces the chassis down, which lifts the axle, the tires unload, the body comes back up, and the cycle repeats = wheel hop.

You do not have to match manufacturer of the brackets to the manufacturer of the LCA, but it doesn't hurt. I like the Spohn stuff, but there is not a lot of difference in the better brands. I also prefer the tubular arms... lighter weight (at least among the ones I have actually owned), and more room for inside edge of the tires. As noted above, if the tubular arms can push a 3,900# convertible to 9.04@155mph, they will probably be fine for most of us.