Drain plug or not, if you want to do a first rate job, you remove the cover.
If you just want to git'r done, you can suck the fluid out of the fill hole. The tool is cheap. And it gets as much of the fluid out as would a drain plug. If you have a lube shop do the job, that's what they are going to do. And that is why you might want to do the job yourself, but if you are not going to go to the extra work to remove the cover, might as well just have a lube shop do it.
And for full disclosure, I've done it both ways, depending on the situation. And none of my vehicles have ever had a plug.