Hello and welcome to the router forum.
My suggestion to you would be saving little more money and buy decent stairs threads MDF has no strength if get wet it will swell, I am almost sure that front the step would crumble or break off, this would be a bad use of MDF
Lot uses for MDF but this not one of them
Looking forward to your participation.
Filling out your profile to include (first name,tools and short bio is strictly (optional )but does help members to better relate to each other.
Thank You John