I own all three fates, so I have had the opportunity to handle and inspect them closely. I do not use them for carry.
Overall they are a well made knife in my opinion with high quality materials throughout. they lock up nicely with little or no discernable play at the pivot.
Are they worth the money? I may get flamed for this, but is any folder really worth $400? Quite possibly not, unless it is a handmade custom and you are paying for countless hours of skilled labor.
Any knife is worth what you are willing to pay for it I guess, I liked the quality of materials used and the shape of the blade, so for myself the answer is yes.
Can you get an as good, or better knife for the same money? Yes, depending on what factors you consider makes for a better knife.
I only paid retail for my Clotho, the Lachesis and Atropos were purchased previously owned, never carried, never sharpened, and I saved a considerable dollar on them. So if you are patient I would recommend keeping your eyes peeled for a similar opportunity.
I also own an SOG Arcitech with carbon fiber scales. This knife shares similarities to the Merc's with titanium liners and bolsters, but has a San Mai VG10 blade instead of BG42 steel, and the aforementioned carbon fibre scales instead of Micarta on the MW.
I believe the SOG street prices for approx. $100 less than the comparable in size Clotho (don't have time to price compare right now). And in my opinion is worthy of consideration as an alternative.
Bottom line though, if you are prepared to drop $400 on a knife, and if the tech specs confirm high quality materials, buy the one that speaks "I want that knife".
You'll be happiest with a knife you like, for the reasons important to you.
Kevin
NOTE: to clarify, the Clotho and Arcitech are closest in size based on blade legth. The Lachesis and Architec are similar in overall open length.