Here is the picture I found on ebay for the same battery BG sells:
2PCS NCR18650B 3400mAh 3.7V Gold Plating Rechargeable Li-ion Battery with Seiko protection board
I do not think they are the same. Button type is already different.
The Seiko protection board is probably the same on the button tops sold by this seller on eBay and on the flat tops sold by Bangood. The batteries themselves are similar but not identical.
Very glad to see a chinese seller bring another option for seiko protected cells (1st option being keeppower). Anyone in the usa can use mtnelectronics.com but for international members shipping might be a bit high.
Could they actually be listening to us? 
i got the seiko ncr18650b from Banggood. the top has a very wide button top, pretty much as shown on the BG webpage, and it is (almost) non-protruding, therefore i would not call it "button top", just "top". this BG photo looks about correct but don't get fooled, the top is hardly protruding:
i don't know whether it fits in Imalent DDT40 or Nietcore tiny monster series, i will test it when i come back home in 2 weeks. here my own measurement: the length is ≤69.4mm, which confirms the BG specification of "69.3mm".
legendary Seiko - Panasonic cell .
I ordered these NCR18650Bs instead 2PCS NCR 18650B 3.7V 3400mAh Protected Rechargeable Lithium Battery thinking that a fraction of a milimeter longer (69.6mm) is not a bad tradeoff for having both raised tops and bottoms which should make them work better when arranged in a line in flashlights such as those that use a battery extension tube.
So far, I have tested them in the new Convoy C8 AK47 7135*8 and they fit well.
I wonder if the flat tops and bottoms you purchased 2PCS NCR18650B 3400mAh 3.7V Gold Plating Rechargeable Li-ion Battery would work in flashlights where batteries are physically arranged in a line? If you have some to test, your feedback would be great.
Thank you.