@wax It comes with a Ti KISS cartridge, which is Load as you Go, or 1 hit at a time. You can technically load 0.1-0.3g, but I find that it works best for me to saturate the coil first, then add 1 hit, or about 0.05g, each time I want a hit. This works great for having a couple hits loaded in separate carts (they weigh nothing, are small, and the price has dropped considerably on them lately), but not so great for reloading in public. For a longer outing, or vaping at home, the hercules gives more consistent hits, holds more, and the parts are sort of reversed (KISS is wire heater wrapped around ceramic wick; Hercules is a ceramic heating element, w/ crumpled up wire acting as a "wick" to hold your oil near it).
The KiSS Alpha Centauri was just released, and it's sort of in the middle between those two options, though it would be ok to think of as a gussied up version of the KISS cartridge -- it combines the globe and cartridge style into one unit, and upgrades the coils. It's still a step below the Hercules, but is capable of working on your current o-phos. If you've only tried the standard o-phos cartridge and haven't picked up a globe, it would certainly be a huge step up, without requiring a whole new battery unit. Actually, even just the standard $15 globe made a big difference for me; the tricks I tried to employ with the KISS carts to get reproducible results just weren't as effective for me as being able to see my vapor. I would stand in front of a mirror and feather the button once I saw vapor forming in the globe, and I could get huge clouds without burning my oil, finally.
Hercules is 7.4v standard (there is a 3.7v heating element, but I don't know a lot about it) and requires 2 AW 18350 batteries (just one battery for 3.7v). The hercules sr-71 heats up faster, and costs $70, instead of $100. It's hidden away in the clearance/sale category on the website. The current gen 74x is easier to service than the 71, holds a little less oil, and heats a little slower. When using mostly to fully charged batteries in my Persei, I get great hits off the Hercules just using the crappy tricks I tried using with the KISS carts (like counting seconds of hit and cool-down) to great success. The hits are usually a nice temp the first couple times, so I have not run it through water, but I'm told water greatly improves your ability to use it properly when first learning, and reduces the temp on those later hits, so you can take more in a sitting.
If you went from a KISS cart (o-phos) to a hercules, just getting one hit at a time won't be an issue (at least, wasn't for me - it gives satisfying, monster rips like combusting from a bong IMO), but the visual feedback one of the nibbler XL's gives must be nice when first learning.