Just bought one of these and it has the ability to mount a press to it. Has anyone ever done this, is it sturdy enought?

I don't have one but it looks like a good idea.
You securely fasten the base plate to your work bench, then the press screws into the base plate. Other accessories will screw into it to so you do have to drill a whole bunch of holes all over the edge of the work bench.
It will guaranty the cast iron base of the press is flush with a smooth surface. Most work benches made out of 2x4 or 2x6 material get a cup warped into it when the wood dries out.
If you tried to fasten the cast iron base to a cupped piece of wood you would surly crack the iron base of the press.
I had to plane the curve off the top of the 2x6 on my work bench where the press was going to be attached to. I would still flatten the mounting area on your bench where you are going to mount the accessory base plate.

I use the base plate and it will work fine for most loading activities and has bolt patterns for several RCBS tools. I've heard there are issues when reforming brass or bullet swaging.

I would have considered it if it was a universal fit. But it only fits RCBS stuff. I also use Forster and Dillon. For them it would be in the way. Good idea, just not right for me.