Immediately? None. A few ended up disappointing me after a while... and one ended up embarrassing me.
There was one I gave my highest recommendation to... and I personally talked quite a number of ECF-ers (and people on other forums as well) in to buying. Mine was perfect for a couple of months... absolutely perfect. Other people reported a variety of problems - and they did so consistently. My guess is that it was at least 80% of the folks who talked about owning it reported serious problems with it... but mine was perfect for a while and I continued recommending it. -- Then, one day, it wasn't so perfect any more. I sent it in for repair. When I got it back, it had every single problem other people had reported with theirs.... It was the VVPV. I still, more than 2 1/2 years later, feel compelled to apologize to anyone I talked in to buying that thing. I honestly feel bad about any role I played in promoting that piece of junk. ---> I genuinely like the guy who made it and his work is incredibly important to the evolution of e-cigs... but I was left seriously unsatisfied with the entire experience... except those couple of months or so when that thing worked right.
I kept it. It doesn't work right, and it leaks like a sieve, and it doesn't charge properly, and I never intend to ever even try to use it again... But I keep that one where I see it almost every day so I can have a good reminder to be far more judicious with my recommendations and to give devices far more scrutiny before I spend good money on them.