For the customer who appreciates...and prefers "Made in America", the extra cost of the Niles stoppers..about 3 bucks is well worth it. This should not increase your selling point by much either.
I looked at the EZ Pots site but could not find anything yet about where their bottle stoppers are actually manufactured. 
If these are made in America, I would expect the seller to share this info and use this as a selling point.
		
		
	 
I'm not going to get into a ******* contest over this, but if you ask them they will tell you where their stoppers are made... I did and they are made in Taiwan.  The quality is very good and I don't find people asking where they are made,  my final product is made in America, I just use a foreign component.  
We are now and will be for all of the foreseeable future living in a global economy.  Adding $3 to my costs over 100 stoppers means adding $300 to my expenses... that's $300 I and/or you could use in our pocket. 
We each have our opinions and I will agree to disagree.... This will be my final posting on this subject.