Newbie here. Looking to buy a Bombtrack Hook EXT from Velostar. Is this a good deal and is velostar legit?

https://action.velostar.us/products/bombtrack-hook-ext?variant=48328719401183&country=US&currency=USD&utm\\\\\\\_medium=product\\\\\\\_sync&utm\\\\\\\_source=google&utm\\\\\\\_content=sag\\\\\\\_organic&utm\\\\\\\_campaign=sag\\\\\\\_organic&gad\\\\\\\_source=1&gad\\\\\\\_campaignid=20358909116&gbraid=0AAAAAoz6g2wbJYQsVEq8UXUzOvQMynlWi

Is this a dumb purchase? It claims nearly half off. I don’t know anything about what I’m doing but my research led me here and I’m about to pull the trigger.

Also, I’m 5’10 with a 35in inseam. So I guess I’m right between M and L? Which size should I pick?