Posted By Steve Hollenbach
In my case with a scope at 2670mm focal length, the 13mm Ethos does a little of both. I would not recommend using the Ethos design to maximize the TFOV when it's a smallish object being observed. However it's a really useful tool in keeping that object or its associated objects in view.
For example, on clear still nights, the 8mm Radian gave me a very good view of Jupiter, but without the moons. The 13mm Ethos displayed the planet very well, but included the moons. I'm sure a 10mm would have done as well. So in that regard the TFOV comes in handy.
If your goal is to observe a very large object, say the Double Cluster (at least in a long focal length scope) then the super wide TFOV of an Ethos puts your eye in the middle. The stars you hoped to see are there, but not well framed. You have to let your eyeball wonder around.
In that case I'd opt for the long focal length EP, and get a more enjoyable view.
For those with fast scopes, the Ethoi have a clear advantage.
For my slow poke Mak, the 13mm fills a niche, but does so very well.