I soooo know where this question is coming from.... I recently had to do a spreadsheet to compare prices from different vendors for the same items.
I'm new to
vaping, but I received my new (inexpensive) adapters today and have been using constantly. I didn't get the specific adapter you mention, but the 901 to 510 adapter is working just fine. I found these for just $3.19 at Liberty Flights. That's less than half the price I saw adapters at another vendor I use (because the other vendor is less expensive than Liberty Flights on other items). If there is a difference, I couldn't imagine what it would be. This adapter does everything it should, has smooth
threads, no leaking, etc.
Maybe someone else will have experience with buying the
same item from different vendors for a true comparison. Sorry, but it would hurt my soul to pay $8 for the same adapter, so I'm unable to give you a personal comparison.
Hope this helps!