I, like many others, agonized over the expense of $70 for a Starrett combination square. I thought there had to be a cheaper way to get there. After spending nearly $50 on various poor quality combination squares, I bit the bullet and bought a Starrett from Amazon.
Someone else said: five mediocre saw blades cost as much as one good one and never cut as well.
As soon as the Starrett arrived, I started checking the other "squares" and found out: a) my two Rockler "clamp it" assembly squares aren't even close to being square b) my 16" Stanley Contractor grade combination square isn't square (bow in the middle) c) my free Grizzly combination square is a smidge better than the Stanley, but still not square d) my Johnson combination square from the Borg is worse than the Stanley and Grizz e) my random assortment of 3 drafting squares are square
I was quite surprised to see the plastic drafting sqaures do so well. Of course, I'm not a machinist, nor do I work for NIST. And I did NOT use a feeler gauge to judge the results. But those drafting squares, from the 5" to the 14", ones were the best I had.
Next on the to-do list, is to order some inexpensive Engineer's Squares from HF and check those out too.
If you're agonizing over a Starrett (or similar quality brand square) and can afford it, do so. You'll finally have one reference instrument. I'll keep the Stanley in the drawer and use it to judge the accuracy/precision of tools I'll use daily.