The "pro" has more options available to you, where the "lite" versions is set up to resemble the oldest menus so the old setup videos won't confuse a new builder with options that aren't explained (and don't need to be touched anyways).
If you can keep your self from fiddling with options you don't understand (hmmm, I wonder what this button does? let's press it and find out) OR you're willing to take the time to learn what the options do and why you'd want to use it, the "pro" is just fine. Otherwise the "lite" will hide options from you that you can leave at default, but might or might not make it better if set right.
The failsafe behavior on a kk2 will depend on what your RX does when it looses the link.
- if it continues to send the last set of instructions, then however you left it, that's the direction it goes.
- If the RX reverts to a "set" failsafe, you'll need to define the settings.
- If it reverts to "neutral" (center sticks, 0 throttle), or reverts to "no commands" the kk2 will stop the motors and the frame will fall out of the sky.
It's easy to test, once assembled (and I recommend you do) -- pull off the props, arm and throttle up to ~50%, then turn off your TX. whatever it does next is what it will do if it flies out of range.
Overall, for a failsafe, I ALWAYS prefer the fall out of the sky, even on controllers that support RTH -- if it falls out of the sky, you almost ALWAYS can find the crash site and recover the craft. Yes, it might be in pieces, but in a fly-away you get NOTHING back, including any onboard video. Also on "controlled descent" failsafes (set low throttle and cut off after a preset-period of time) the craft can drift quite a ways, and might drift into a crowd . . . with motors running -- the point is you have no control and you're letting the controller continue to fly without input from you.
If you're not flying over people and you loose control, if the motors cut off, your chances of injuring someone and/or loosing the airframe outright is practically nil. The longer those motors run and the longer the craft attempts to fly itself without input from you, the more each of those chances increases. IMO, not worth the risk.
