Funny you should ask. I just unboxed my new Marksman and I am mightily impressed. It is solidly built, not too big but pretty heavy, and the cycling is the smoothest I've ever experienced. I placed it next to my Forster Co-ax (which it will replace) and the MEC is even silkier than that.
If I could distill what I like about the MEC into a single word, it would be "simple". I want a single stage press to do one thing: move a shell holder up and down. I don't want it to prime...there are better machines for that. While I appreciate the engineering of Forster's "universal" shell holder, it's not universal; switching between the "large" and "small" orientation can be a circus of flying springs and three-handed maneuvers.
The one thing the Co-ax may do better than the MEC is capture spent primers. The MEC drops them out of a slot milled into the back of the ram and into a tray that sits on a bracket under the main body. It's a good system, but you pretty much need to have the press up on a stand to provide room for that little tray underneath. It's a limitation I can live with because I think the press that good. If you decide on the Marksman I don't think you'll be disappointed. (And that price is excellent.)
Thanks for a detailed overview of the Forster and MEC, I don't have any single stage presses and when I get into rifle reloading was planning on getting one with a floating shellholder or floating die setup. The MEC is a lot less than the Co-Ax and, like you, I don't need a priming system on the the press either, would rather use a hand priming tool instead.
Which brings me to another point about universal shell holders. My RCBS hand primer is universal, but there are times some cases will not hold still while priming and fly out, probably due to tight primer pockets, maybe because of the universal holder. Whatever the case, if a standard shell holder were used, it wouldn't be an issue.
As for spent primers, I deprime before I clean the brass and encourage others to do the same to get the cleanest primer pockets they can. So the MEC's capturing of spent primers is a non-issue.
At over $300, usually $340, the price of the Co-Ax is on par with mid-range progressive presses. Does it make ammo more accurate than the MEC does? Doubtful. Is it a more complex design than the MEC? Yes, and that's where the cost comes from. The MEC is as you say simple and not only simple, it looks a lot stronger and could hold up to some heavy duty case forming whereas the Forster probably would not last long, nor would be as nice to use given the ergonomics of the handle.
I won't bash anyone who has a Co-Ax, but I have to say in my limited time reloading that if anyone is like me looking for a similar style press, the MEC is more bang for the buck.