They are the primary company that I have make mine. The ones you are looking at will not work with the tall spindle.
The off the shelf ones are made for circle track racing. They are set up for stock spindles and a little different for use on a roundy round.
They are very similar to a stock arm and you can't get it to align right or work properly with them. They also have steel bushings instead of teflon. The ball joint is in the totally wrong place and at the wrong angle.