Best Ebike under 600 Dollars

I am looking for a 500 dollar ebike that is actually UL Certified and wont catch fire. Calfinrofnai rules prohibit certain ebikes. I have come across the 5th Wheel Mate for 500 Dollars which also claims to have ul certification. Also the Walmart Concord Folding Ebike. Walamrt concord is 450 dollars and has 350 watt motor and 20mph. The 5th wheel mate goes 23 and is 500 dollars. Are they safe and for the 5th wheel mate does anyone have experience with it and or customer service? Thank you in advance