The horizontal coil is further from the mouth so the vapor is a bit cooler and the mouth end stays a lot cooler. In additional the stuffing in the Volt and Bloogplanet cartos is especially absorbent and my juice (around 80PG/20VG. just like Volt juices) goes right in. They also have a smaller air channel and seem to have a bit less chance of leaking and also give a big drag more easily (good stuffing, fast wicking, uses juice a bit faster)
The V4L cartos have a coarser stuffing, a bit more tightly packed, that is not quite as good at absorbing/wicking nor letting air flow through it, but have a bigger air channel. They are significantly hotter at the lip end and may be a bit lower ohms. I actually think the flavor is conveyed better by Bloog/Volts cartos but the nicotine hit may be stronger with V4L. I use both. When I was on higher nic I actually preferred the V4L Coolcarts and found the heat/hit of the WOW cartos too much w/ 18mg juice. Now I prefer the V4L WOW carts (with a plastic drip tip for a mouthpiece) and the Bloogs (and I think I like the Bloogs a bit more).
And there are other kinds/brands of cartos too and they are all different. And the hotter ones (below 2.5ohm) are not meant for slim ecigs at all and are only for fat batteries 450mah+ and mods, and the ones above 3 ohm are usually meant for high voltage mods.
One kind that is very similar to Volt/Bloog cartos and may or may not be identical are Kanger KR808D-1 2.6ohm Horizontal Coil Cartos.