A Boge 510 cartomizer lasts me about an hour (when I vape constantly, which is often). They are very easy to refill -- just pop off the end cap, drip up to 16 drops into the filter, put the end cap back on (I use a large paper clip), and vape.
An eGo Mega cartomizer lasts me about 1/2 hour (when I vape constantly, which is often). They need a syringe and needle to refill. I fill until it starts leaking out the needle hole or the threaded end hole. About 1/2 hour of constant vaping, I get a burnt taste, even though I can't believe it's almost empty yet. Also, the taste is inferior compared to the Boge 510 cartomizers. It doesn't have the flavor I get from the 510s. So, I quit using them.
Now I'm using only the KR808D-1 Premium cartomizers, which are similar to the Boge 510 cartomizers, except the threads are different. These fit the KR808D-1 passthroughs that give me throat hits every single time, and much better flavor and vapor than I get from the eGo 1000mAh batteries and Boge 510 cartomizers.