Would this be a good choice to apply stain to my house siding?

The Control Spray Double Duty is designed to spray thin bodied products such as oil-based stains, varnish, clear coat sealers etc and could definitely be used to spray your siding with one of these materials. If the stain you want to spray is a latex-based solid stain you may want to take a look at either the Flexio 590 or the Flexio 690, which are similar to the Control Spray Double Duty but are more powerful. Both of these sprayers are less than $200. Note that all of these sprayers will spray from a quart or quart and a half container that will requiring refilling. An airless sprayer that can spray at a more rapid rate and draw material directly from the can or bucket may speed up the project.