I had one of these. Other than arriving dented and scratched it worked just fine. Though I was moderating only 18v on a 12v system. I ended up just removing it since it didn’t seem necessary since our ride-on had low/high speed shifter which brings it down to a manageable speed even on 18v. I did also use PEMENOL Motor Speed Controller... https://www.amazon.com/dp/B07WR4KBMF?ref=ppx_pop_mob_ap_share and it worked well to reduce the speed, but I really got it for the “soft start” feature and could never figure out how it worked, so I removed it. It did seem to be of quality construction.

Edit: this module does not reduce voltage, but simulates the same effect. I’m not sure if there are any long term implications, but it’s design to control motor speeds.