I have wanted to know the opinion of a few old school knives myself, not all the ones you stated but the Douk Douk, Svord peasant and opinel.
I have both an opinel and a svord peasant (just got the svord) but can't speak of the Douk Douk nor mercator.
To begn with I have said before that my opinel sharpens easier and likely gets sharper than any other knife I have...but the svord may get as sharp (maybe sharper), but its a little more work because of how poor the blade was ground. The blade of my Opinel is perfect, and with very little effort its like a super razor...the svords uneven grind makes the sharpening a longer process, and is far from perfect, but it shaves with great ease.
Using the svord in the kitchen however it falls short of the opinel, even with it shaving hair with equal ease it just didnt cut various foods as well.
The svord is also a lot thinner than I thought, it very very close to my Opi #8 in thickness.
The svord is really more garden tool like than pocket knife like...where my opinel has class my svord (w/plastic handle) is more a tool thats treated like a rake or shovel. I am sure this feeling of mine is because I don't have a wooden handle, and it would have some class to it if it did, but I don't think it would lose that garden tool feel.
The ease of opening and closing the svord lend its self to work more so than the opinel, but I don't think the svord will replace my opinel for weekend/leisure carry and use.
I like the look of the Douk Douk very much, and it will be my next knife buy.
I will continue to carry and use my Opinel #8 (I do feel its a little on the small size) on my weekends as it has class and a wonderful blade. The svord will be tested more and hopefully I'll clean up the grind and perhaps make a better handle? it should make a good pack knife at least, something stuck in a bag and forgotten about untill its needed. Something that can be beat without mercy (if it proves worth beating). Point being its crude as is, I don't look at it in the same light as the Opinel.