during normal use, I have yet to see any lag, and I have a good number of large games installed such as gta VC and CTW, hearthstone, Goat simulator and pocket mortys, all of which experience no lag.
I can get roughly 3.5-4 hours of screen on time with normal use, usually revolving around facebook, youtube, tumblr, online shopping and web browsing.
In terms of the fingerpring scanner, from pressing the power button, placing my finger on the sensor, and it finally unlocking, it takes just about 1 second, and most of that time is just the screen turning on, once its on, its practically instant.
in terms of temps, as i'm feeling it right now after using it for some youtube videos, it just got barely noticeably warmer, the only time it actually does get warm, is when in use with a fast charger.