Doing a new house build in a beach area (ie. hot & humid) in SC. I have to decide what to use for the steps to my 2nd floor bonus room. One vendor is saying use White Oak and stain it. Another says to use the same engineered hardwood that is covering the entire first floor. The white oak/stain method sounds way more expensive. Why wouldn't I use the same engineered hardwood on the steps. It seems cheaper and it's an exact match. What am I missing? It's 17 steps straight up and down with a landing at the top. Nothing fancy.

The advantage of using pre-finished wood like what is downstairs, besides being less expensive than finishing in place, is the finish that is on pre-finished is much better than what you can buy and apply yourself or by a contractor.
The drawback is that the nosing finish may not be available or will not match the finish on the flooring. You can always make brackets or scotia to get close to a match of the pre-finish flooring to make great trim for the steps.

thank you. Will I have any trouble installing a handrail on the pre-finished engineered hardwood?

Install the flooring on the steps, then cut with a multi-tool for the post on the first tread. Drill into the flooring or nosing and dowel the top post.