They are indeed the exact same product. A few years ago, I compared their products side by side in-hand. Same thing.
I actually *really* like the "Diamond" bags...the material is clear and much easier to fold, as you mentioned.
Just understand that it is not Mylar...even the word Mylar is trademarked - it is a very specific composition. As stated, the Diamond/Clearbags product is BOPP (10% recycled).
If this is not a concern, I wouldn't worry....but save yourself some money by buying from Clearbags! You're getting ripped off on eBay.
There is more than one thread about this on the boards. Google it up and start reading.
DISCLAIMER - I am not involved, nor have I ever been involved, in the manufacture or selling of comic book storage materials. I have no personal contact or influence with any of the companies or products mentioned here. I am simply a consumer. For the record, I did use the Diamond/Clearbag product. I had over 400 slabs sitting in those bags at one point. Now I buy legal-sized Mylars from E. Gerber. They are more cumbersome to fold...as Mylar SHOULD be. It's a very, very strong material (more tensile strength than STEEL).