I just got in two Echo-e cartos from Cropduster and a beautiful stainless GoGo kit from Billb! Very happy at this point with both the vendors and the items. I've been using a true 3.7 Ego with Dual-coil 1.25's and loving it, so this is what i compare both to, using the same tobacco @36mg, 17%vg that I love from Tastyvapors.
Voltages on the Ego and Gogo were at 3.9 noload, ohm rating of both the Echo-e and GoGo carts were 2.7, I plugged the bottom ends, filled via syringe and did a mild taryn spin to settle the juice. I got a bit over 3ml in the GoGo and only 2.5 in the Echo-e. Vaping wise, I find the Echo-e produces slightly more vapor than the GoGo in the beginning, and slightly more than the Dual's on the Ego. The GoGo was too airy for me so I blocked two slots with electricians tape, now it's perfect for me. The Echo-e carto is much quieter than the GoGo and a little quieter than the Ego with DC's. Right now (1 hour later), They all seem to produce about the same vape and I can't tell any difference in taste at this point, but my buds could be fried again too.
None of these produce as much vapor as the little 5v Foxy box mod though! So now I know that 5V is more powerful and produces more vapor than any 3.7 device using any atty/carto on the market (that I've tried).
Bottom line on these; I like and will used them all! I guess the next move is to try some fruit, coffee and cigar flavors on all three and compare.