There you go. No doubt about it, only one solution: Buy 'em all.
Each has it's points. O-phos supports basic use but is limited and of a lower quality overall (being basically a modified e-cig battery), you should expect it to die......then it won't disappoint you.
Omicron can drive the higher producing carts (even the 1.5 is questionable in O-phos, the rest are out of the question. If you ever get more than six feet from a USB port or wall outlet the ability to swap fresh batteries into your Omicron and keep on vapin' won't benefit, but most find this a prime step up.
Persei takes this a step further by carrying a lot more battery on board (say 3 or 4 times?) and is therefore not only an advantage in time between battery charges, but it has enough battery on tap to drive the big boys (Hercules, Bender, and no doubt fun stuff in the wings) should you tire of oil carts. Or just want to screw a different top on for the afternoon. Persei makes it effortless to use, Omicron requires a little more attention, although it's button is easier to work. A second head for double carts is a nice plus with Persei, many have found it useful to keep going while their single was being serviced (you can run one cart only if you want).
Tough call. Only sure way is one of each, really. Otherwise, the most expensive does the most and does it best....as you'd expect?
Good luck with your choice.
OF
