I've owned both.
The ESEE-3 is heavier than a thin bladed 3.5" fixed blade needs to be. I dig the design, but it's handle heavy and balanced poorly making it feel heavier than it is.
The M10 is great. It's thin, light, designed brilliantly and built carefully. VG10 is good enough, it stays sharp, touches up easily, and doesn't rust. I use my M10 as a lightweight utility knife for backpacking and hiking. The sheath options offered by Cutlery Shoppe are excellent. I thought I wouldn't like the kraton hard plasticy handles, but after using them for a while I'm finding them to be perfect because they're grippy, keep the weight down, and they don't "hang up" on light fabric like a t-shirt. It carries well in a pocket, on a belt, or inside of a waistband. Also, I believe it has the same DLC coating as Spyderco uses, mine has held up very well and still looks new, even after being used quite a bit.
The M10, in my opinion, is the fixed blade equivalent of the Spyderco Endura - a lightweight, durable cutting tool that represents the maximum amount of value you can get in its price range (actually, I'm pretty sure that the Gryphon knives are made at the same factory as many Spydercos and Fallknivens are).
