This is just my own personal experience, but using an LR Mega atty with my USB 650 battery lasts WAY longer [1.5 days with moderate
vaping] than using it on either of my 2 900s [about 2-3 hours with moderate
vaping]. I'm not sure if it's because I got the USB 650 from a different vendor, or because it's a USB charged battery, but LRs generally will shorten the lifespan of the battery.
It's a factor, but if it works for you, then great. With my 900s, I have an LR 306 Cisco on one and a standard eGo Mega atty on the other, and both retain over a day's worth of battery life. It's just the LR Mega atty that drains 'em.