Those are rated at a much higher capacity than other batteries of a similar format which would make me wary, and when taking into account the space lost to the built in charger they claim a much higher energy density than 3.7v 14500 li-ion batteries.
There are some EBL batteries on Amazon UK which have a similar capacity rating, 3300mWh but a couple of the reviews (1 star :D) state they only produce 1500-1700mWh on a discharge test, which would make more sense, i would assume the same for the Epoch batteries but having never tested them i can’t say for sure.