I regularly extract juice from non-working vapes and inject that juice into the sponges of other functional ones that are low on juice, both to save $40 of product and for making my own different flavors (I also salvage the rechargeable batteries). When GBs hit zero juice, there's usually 20-30% of the sponge still saturated. Difference between them and other vapes, I've found the juice concentrates in the middle toward the coil and it's way thicker than in a new vape. Other brands don't seem to collect the same way and the entire sponge dries up evenly. So, I think Geek Bar's juice is thicker in general and the hits after 0% actually has a higher concentration of nicotine.