A dado would work fine Rob.
Some dado blades don't make a perfectly flat cut, and may have slight little 'points' ground on the outside edges of the outside blades. Not really a big deal though.
These box cutter blades though also make it very easy to dial in the 2 widths without having to adjust with shims. Put them together one way and you get 3/8", the other way, 1/4".