I have both and the Ratmandu has much better ergos like Worldwood mentioned, also I think the clip/sheath combo of the 6 might look better on paper but I replace a ton of them... the clip itself (any clip?) is handy though and makes taking a sheath on/off pretty quick. The word "ESEE-6" could be replaced with a bunch of other knives in that size range and once you compare them to the Ratmandu... in the ergonomics dept. it's not a fair fight.
________________________________
To the sheath question: Yes, I do.
I have a clip that I attach to a backing plate that has a drop & offset to move the knife/sheath down and away from the user. To me the biggest advantage is that you're not confined to a pancake sheath so you can have a Ratmandu Taco Sheath with a drop/offset clip mounted to the back of it.
From the front it's a little smaller than a lg. Tek-Lok: (ESEE-4/Candiru)
View from the back:
Same Clip different setup/front, side & back: (ESEE-5/Candiru)
On a taco sheath it's a great/slim setup: (TOPS BOB)
If you're looking for a Clip setup that sits the knife higher a plate can be made across the back: (SRKW: Rodent Solution) Finally, Swamp Rat content!
This thread now needs a picture of a Ratmandu:
Hope this helps,
Eli