Is this cheap Track Saw Square worth it? 

I've had one for about a year now, works as advertised. Makes quick work of breaking sheets down and keeping things square.

Works perfectly with my Makita Track saw, was out of the box dead on 90. I mostly use my track saw to break down sheet goods and do all the final cuts on the table saw but recently used it to square a table top and it worked perfectly, highly recommend it!

A few comments if that is okay. Take a scrape sheet of plywood that you know is out of square, and cut all four corners the same length. For example a 2 foot square. 24 inches all the way around. The measurements from one corner to the opposite corner should be exactly the same length on each corner to corner. Yeah the TSO squares are pretty darn expensive, but their motto "Born square" is there for a reason. Also the TSO squares allow you to attach some pretty nifty rail guides. If you plan on doing a bit of repetitive cuts that have to be dead accurate, TSO is the way to go. Good review.

I think you'll find the framing square used for the comparison might be less accurate. Like you say it should be good enough for most application and I'll be looking for one for my track. Both slots on my track face down so it's a little tricky finding one.

I paid $25 for mine and it works perfectly. My clamps I use with the 110" Wen tracks also works fine.