For a start because they have a charging & USB socket in the end of the case they are a lot longer than a standard battery.
If the BMS spec is correct and discharge cut off voltage is correct - 8v the battery will be long dead before it reaches that.
They use Pouch cells which I don't think are the best there are pros & cons with them.
I would give them a miss, have a look at Fogstar they use EVE prismic cells and about the same price with discount (offered 15% to Funsters)
Contact Ecotree Lithium batteries. An English company
i have had two off of them and they are brilliant. I am sure they are cheaper than what you quote. PLUS they give a Discount to MHF members. Not quite sure of the contact numbers as in France at the moment. I think this the one you will need.
It really is a potential minefield out there re lithium batteries
There are so many offerings that it's difficult to wade through them all.
My search criteria was based on type of cells (i wanted EVE but there are others rated just as highly)
A long guarantee - 20 years if poss
A good company in terms of easy to communicate with an do they respond to messages in a reasonable time AND no adverse comments from buyers
High rate of discharge to cope with a microwave
and of course price per Ah !!
If i could also find any YouTube videos about them or their products then that would be a bonus!