Are All 2x2 The Same OR Is There A Difference?

Just buy from a reputable coin supply dealer like Wizard and you'll be fine - the good guys use acid-free cardboard and mylar for their 2x2s.

regarding glue/staples, I think you'll find that most people here use staples (this opens up another discussion on flat-clinch staplers ).
Not entirely sure what you mean by DIY 2x2... they're so inexpensive that it wouldn't be remotely worth it IMHO.

As far as amount to buy before discount is negligible, I don't know. I am still working through the stacks in various sizes I purchased a few years back. Don't use them very often - most of my coins go into albums.

There is a difference. I remember having some a long time ago where the Mylar,if that is what it was was had a milky look to it instead of being clear. The cardboard was also a little yellowish instead of being white. The cardboard was also a bit thicker than it should have been. Nowadays they are mostly good quality but once in awhile I will come across one where when you fold it over it does not line up properly. As to bulk prices,check eBay. A pack of 100 is around $3-4 U.S.
John1

If you notice those cardboard 2x2's do not have a manufacturers name on them. Made in many places by different companies. Some are slightly larger and/or thicker than others. With out documentation, you really don't know what the plastic or cardboard is made of. So yes there are differences.