I can't recall the name of the brand that Oreilly's sells, but I remember reading a test on lower end gauge accuracy and they were off compared to Autometer/Stewart Warner and such. Not sure if those would fall in the same category, but the link was specific.
I'll see if I can dig up the article.
EDIT:
Equus was the brand that was compared. I can't seem to find the article though.
Yeah, I'll end up getting autometer. I saw those and figured I would at least get opinions. I know you get what you pay for but it wouldn't hurt to check. Lol