best 4 stroke kit

I'm brand new to motor bicycling. I have a sixthreezero evryjourney bike (https://www.sixthreezero.com/products/evryjourney-mens-touring-hybrid-matte-black), I want to install a 49cc or less kit. I've been looking at KMB, BikeBerry, and most recently, Golden Eagle. I'm trying to compare a kit...