Hi Yen and welcome to the Forum!
It seems that you are new to the forum, so I will answer your question as if you are new to Fast Tech too.
On today's page 1 on the FT site under ecigarettes, there is an "authentic mini protank 3 dual coil" listed for $6.92 american dollars.
It says it has 93 reviews and a 5 star rating.
If you click the image it will take you to the correct page.
Scroll down a bit and you will see headers telling you "reviews" and "discussions".
Click them and you will probably find out a lot not only about that exact item, but especially in the discussions, you will hear people comparing it for better or worse, to other similar items sold on FT.
Sometimes FT sells items that are called the same name, look the same, but are not the same because they are made in different factories, or by different manufacturers and will have different SKU numbers to reflect that. The quality can vary widely.
The discussion threads are wonderful for sorting it all out!
ECF is great too, but where Fast Tech is concerned, just knowing that others are talking about the exact same model/manufacturer that you are interested in, can save you from many misunderstandings!
I hope this helps you. Good luck and happy vaping!