Last I heard it was only the echo and echo-e which stands for echo-ego, meaning it is a 510 model and a pushbutton. There is also an echo cart for push button models that use 808 threading but it's hard to find. (I believe it's called echo-v for the Vgo) I am totally unaware of an echo vv.....but that would be AWESOME!!!!!!
There are so many good 3.7-4.2 510 models that I can't see any reason to recommend the echo-e over the riva/KGo especially because the reviews of the echo-e cart are lukewarm at best. Why the 808 echo cart surpasses the echo-e cart is a mystery
The only reason I bring up the echo at all, is because I am just about as annoyed as Morandir at hearing what an inferior unit the 808 is and that all automatics are noobie crap. My automatic fat batt echo is the best and most convenient pv I have used when it comes to vaping on the go. Even right now I am typing with both hands with my 650 gripped comfortably in my teeth, vaping away! I can fiddle with stuff and vape. I can tear apart a house and rebuild it while vaping (if I knew how to tear apart and rebuild a house) I can drive with both hands on the wheel and vape. I can drink through a straw and...ok, that's enough.

.......
(breath).....

aaaahhhhhhhhhhhh. I'm better now
I only wish we could move the echo thread to the kr808 section so folks who like kr808s can see a good upgrade option instead of lumping it in with ego type batteries where it is lost.
And sometimes. I still like to leave the house (when I am only going to be gone for a few hours) with just my kr808
That is all!