Loading it one time for 400+ hits isn't a huge deal. You can do 4-5 cartridges in less than 30 minutes if you take your time, that should have you good to go for a while. And while I get where you are coming from, implying the Omicron costs more is way off. It definitely is less expensive in the long run because it works so efficiently.
The other vapor pens look more stealthy, true. But I've had no trouble using my Omicron anywhere, inside or outside. Some people look at me but they don't understand what they are seeing, but they leave me alone lol. That happened with my iVapor, too. The Omicron has a higher learning curve to setup and use properly, that's all. But I've had mine for a week and I know how to get tiny, stealthy rips in just a few seconds. I can also achieve massive rips, which I wouldn't recommend on the other vapor pens because it'll start charring up the cotton and the tubing.
And the cost of those other cartridges.. if you were to take a lot of big rips from those cotton-based cartridges, they'd die incredibly fast.. I'd have gone through 5-8 iVapor or Gentleman's cartridges in the same situation I went through 1 Omicron cartridge. That 1 cartridge cost me $50 to fill with high quality puddy. You'd pay $200-300 for those 5-8 iVapor/Gentleman cartridges, which are composed of a glycerin-based product instead of a pure concentrate like the Omicron.
Basically, once you get past the learning curve of the Omicron, only the stealth-factor is an issue. That's just because it's a little bigger, and it's shiny. With the amount of money you'd save using an Omicron versus other vapor pens, you could afford to give it a professional paint job, like a black matte appearance similar to iVapor's, and still come out ahead.
Maybe you see it differently, that's cool.. Maybe the stealth factor, even only a little bit of difference, is an important consideration for what you are looking for. But you are going to pay a lot for more that little bit of stealth, and everything else about those products will be inferior to the Omicron. Keep that in mind!