Just my experience here:

1. The brownells $100 wall gauge is nearly unusable and gives rough estimates. (owned and returned one)

2. The hosford gauge is so-so

3. The galazan gauge (just like the type used at every famous maker) is expensive but idiot proof. I love mine.

4. Truth gauge only does about 6" of measuring making it a poor tool unless the goal is crude estimates at gun shows.

Long story short, I found anything short of the classic wall gauge "towers" to be a big disappointment.