I vape each Blu Premium 100 cartridge until I get the first hint of a different taste (indication of a nearly finished cartridge). As soon as I sense the taste change, I seal both ends of the cartridge and set it aside for future use. I save all my used premium 100 carts and when I have 4 finished ones of the same flavor, I do a reverse taryn spin on each. I get enough juice out of the 4 cartridges collectively to refill another entire cartridge. The refilled cartridge tastes just fine, as long as I refill the empty cartridge with the same flavor it originally came with. Saves a little money and I get 6+ cartridges of Vape out of each 5 pack purchased.
Even if you vape a Blu cartridge way too long, until it tastes like crap, you can still get a little juice out of it with a reverse taryn spin. But removing the liquid after you get a really burnt taste will make the resulting liquid you extract taste like crap too. So it makes sense to stop vaping the Blu carts a little earlier, save the used cartridges instead of throwing them away, remove the plastic end cap & underlying rubber ring, extract the liquid, and then use an eyedropper to collect the liquid and refill one of the empty cartridges. Just make sure when filling that the drops don't go into the center hole which is where the atomizer is located. Hold the cartridge at an angle and drip onto the side walls in order for the liquid to saturate the cotton filter which will avoid the center atomizer chamber from getting wet. Use a tack or paper clip to pull off the plastic end cap after your done with a 1 piece Blu cartridge to see what I'm talking about in regards to the center hole . . . .
And if you ever get a dud Blu cartridge that doesn't seem to work, you can use this method to empty the liquid from the cartridge and use an eyedropper to transfer the liquid into another cartridge. No more worries about dud cartridges.
I use one of the rubber end cap sleeves (condom) that comes with the blu disposables you find at retailers. It's used to catch the liquid that is extracted from the flavor cartridge during the reverse taryn spin. The plastic sleeve from the disposable Blu's fits the Premium 100 flavor cartridges pretty well, although I do add a small piece of tape to keep the condom from moving during the spinning process.
You can also look up 'reverse taryn spin' on youtube to see the method for extracting liquid from a cartridge.
Just my
PS: I'm doing the above with the one piece blu premium 100 flavor cartridges. I am not familiar with Blu's other cartridge products and don't know if the above info applies to the cartridges from their other product lines such as those from the standard kit as well as the older 2 piece cartridges).