Given a choice between the e-Power and a Riva, I'd take the e-Power any day. It uses a bigger battery, batteries are cheaper to replace, and freshly charged it'll give you better than 4v. madvapes carries them here E-Power Replacable Battery eGo kit! for $45.99, pick up some Clearomizers and you'll have basically the same type of setup. It's a few $$ cheaper than Provapes too, and madvapes is an ECF supplier too.