Ok, unfortunately I have changed my opinion on the product. I now think they are only good as a better-than-throw-away option for someone trying to quit.
I had what I believed was a switch issue with the first one I bought and was about to return it when my second one broke. A friend tried to be helpful and take a look at it and the whole blasted thing disintegrated. I found out (fortunately before I had to pay return trip postage to have them looked at) that the first one had been dropped, and that is most likely what broke it and caused the connector to get ....-eyed.
Not necessarily poor or shoddy design, but you do get what you pay for. I have dropped my Prodigy V3 a bunch of times over the past two years and it's still ticking. Easy enough to say "well they aren't designed to be dropped", but round objects are likely to roll and falls are likely to happen. I have to consider normal "life happens" kind of stuff like that when I'm deciding whether a product is useful to me or not.
Also, although I originally said the 17670 fits fine, I wouldn't recommend it. Seeing how fragile the plastic construction really is, I think the stress of anything other than an 18650 contributes greatly to the breakdown of the connector, as mine got wobbly not but a day after I wrote the review... the subsequent drop probably did it in because it was under too much pressure.
So, yes, I think they're a very affordable option, but probably don't have the stamina for long-term use by a vaping enthusiast. That said, they are still my #1 suggestion for the "I want a mod to help me quit smoking" newbie. If they stick with it and decide they want to switch to vaping (instead of just stop smoking) then I would recommend a beefier mod like the metal Bolt which I am now the proud, and happy, owner of two.
Btw, while the initial product I went to gotvapes.com for was a bust for me, I am still a very contented customer as their customer service was top-notch, shipping was quick and prices are among the best I've seen.