This may just be me, but I want a Hinderer for the reinforced spanto tip. To me, it's the one thing that really parts the XM-18 from its many competitors. Without that super strong tip I have no interest. The customs that I've seen with a bowie style or wharncliffe blade look really nice, but they don't look like an XM-18 to me. The slicer grind is good for some I guess, but I can carry a dozen other knives that will slice just as well or better than the XM-18 slicer. I have a XM-18 spanto because it is the only knife (that I know of) that offers such a grind. That's what the man had in mind when he made the knife and due to requests from customers he started doing different blade patterns and grinds.
The flipping action of the XM series will never be on par with the ZT056X series until Hinderer starts using some bearings in his pivot and offering a way stronger dentent.
I've had no problems using the thumbstuds to open my 0561, but I can see how some would have an issue with using the thumbstuds. I've put that knife in quite a few hands of non-knife guys and almost none of them can use the thumbstuds to open the knife. You have to fondle it for a while and get used to how it feels or you have to be very familiar with knives, flippers in particular.