I've ridden a Swoard EC Pro 2 as my EC board for the past year - so my opinion here is based on observations about how it behaves vs. my other boards.
Main EC priorities:
Fat waist - allows for less severe angles without boot-out.
Torsional rigidity - but longitudinal flex. You want to be confident in the edge and balance - but the board needs to de-camber (especially on stiffer terrain) and flex consistently at nose and tail.
Large constant-radius side-cut. Long stable turns.
There are certain properties in the board I'm not sure are necessarily "EC" - but I very much enjoy. For example I don't feel like I need to load the tail too quickly - whereas on my Prior 4WD I needed to slam my weight to the rear almost immediately in a turn. I'm not sure what makes this difference (something about center position or flex?) - but it's quite a noticeable difference.
I ride it exclusively now for hard gear... it feels amazing in every (reasonable) condition. You can absolutely ride it upright. I switch between styles depending on the terrain. EC is fantastic on steeper terrain because it's extremely smooth/stable and capable of controlling your speed. On flatter terrain I'll ride more upright "race style" to jump into the turns and load the board/pop-out of carves for speed and then use more EC style to shed speed and alternate as needed.
There is one caveat... it's not a "fast" board at all. It's design to set an edge aggressively... not to go straight. On very flat terrain or traverses it has a tendency to drag the tail - due to the long contact points, side-cut, and shape - and it's the first board I've owned that does it. I couldn't care less - because at that point I'm just trying to get to the steeper terrain or lift or whatever - but it's slightly annoying.