I think that a large part of the popularity with Halo is that they offer good gear for a "mainstream" hardware and ejuice company. While it is true that there is nothing extraordinary in terms of the batteries/clearos/etc. that they sell, they do theior homework and match equipment that works particularly well together.
This makes Halo attractive to new/newer vapers that may not really understand the nuances of matching batteries/tanks etc. Keep in mind that Halo is not aimed at vapers looking for mods and more esoteric gear...more for folks who just want to vape and not get immersed in the details of vaping.
BTW Completely Average, Halo does not manufacture anything...the batteries, clearos, chargers, cartomizers et al come from China...but they do spec out to quality manufacturers such as Kanger. I am in no way saying that their gear is of poor quality, but no, they do not manufacture it, they purchase from China and put their logo on it, as with most ecig companies.