you really don't want to use an annular cutter if you are drilling hot rolled or rusty plate at 7/16. the annular cutter will dull really quickly on scale or rust, and resharpening one isn't nearly as easy as is a twist drill.
the big advantage of annular cutters is they remove less metal for a given size hole than a twist drill, and take proportionately less feed pressure. that advantage is basically lost under 1/2", and they cost a lot more too.
as a way of visualizing the work savings, the size of the slug is a good guide. I don't know what size the slug is on a 7/16 slugger, but it can't be much more than 1/4 or so, meaning you are saving the effort of drilling a 1/4" hole.
It would make sense is if you were set up drilling larger holes with a mag drill, and had a few 7/16 to do as well. it would save setup time to pop one in.
I don't have a specific brand/model recommendation but make sure it has the upward travel to fit the chuck and the 7/16 twist drill.
happy drilling!
P.S., do get a unit that takes annular cutters (3/4 weldon spindle), and a auxiliary Jacobs chuck, so that you can use the slugger bits in the future when drilling larger holes!