If you think of it in terms of cars...
Mitsubishi makes the Lancer, now imagine if Toyota made a Lancer too... and VW made one called a "Vancer". A lot of that is going on, but now imagine there are also a lot of companies that actually
buy the Lancer from Mitsubishi but pay to rename it whatever name they want and add their own logo.. that's happening too!
It ends up being really hard to discern which one is the original Lancer and which one is a copy, in the end it doesn't matter as long as it's made by a good manufacturer.
I know that Totally Wicked's Tornado is a real Joye eGo, so is Ovale and Inferno. Riva is a knock off but it's a good one. Vgo I have hear ok news about, kGo I've not heard good things about... Then there are look-a-likes that aren't even 510 compatible too...
My best advice is to google 'ecf + the name of whatever you want to
buy' and see what comes up. Barring that I see no reason to
buy anything except a genuine Joye eGo from a proven ECF supplier or a Riva (which is only $30 after the 20% discount). It's not like you're going to find a better deal than that.