That particular blue pack is so fake. I've pointed out numerous times how you cannot fit 20AH in a 52 cell battery, nor can you sell it for 100 bucks. If they were to rate it honestly, maybe 8AH new, and it would be OK for a smaller 250W-500W motor.
Anyway, battery aside, that is the sketchy side of ebiking. Very fast bikes with squonky brakes, Batteries mounted with zip ties and duct tape. After a while, pride of ownership kicks in and people try to make it look decent.
Here's my $350 ebike. Bike was from neighbor's trash. $200 ebikeling 500W geared motor. $100 surplus scooter batteries (36V10AH) on the rack. Won't wheelie and won't go 30 mph. I later bought a 48V12AH frame battery for $450 (so I could sleep at night) and gave it to a relative.