Compatible OS Android 5.1 or above; iOS 10.0 or above, Brand KOSPET, Operating Mode Full-Touch, Product Name TANK M1, APP Name Da Fit, Bluetooth Version BT 5.0.
Basically copy coupon, view price history or create e-mail price alert. What is the best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. Only one coupon available!
Link: Banggood product page
1. ($55.24): BG284c49
put item in your cart and apply coupon code there after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): TANKM1FANS, BGd086ee, BGJP99333, BGb227a5, BG8ede1d, BGb9bac2, BG6ad230, BG87a8a2, BG95b8a8, BG8f0384, BG14b8f3, BG4faf7a, BG6b13a6, BGJP116, BGbf11dd
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for KOSPET TANK M1 Smart Watch. The lowest price was: $39.99.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).