Gary, the voltage cutoff I think is built into the EVX2, but I dont think it it built into the original EVX. ( i mean, it MAY be, but I dont think so)

as far as needing 2 of them, I would have to let a emaxx professional answer that one.

I dont have voltage cutoff on any of my rc junk, becuase Im usually tired of doing laps by the time the lipo pack starts to poop out. I frequently check for tempature of the ESC and motor as a guide.

I only had one bad expierence with the lipo, and it was all due to user error. ( i hit it with 3amps on the NiMH setting. almost had a fire, but caught it before it burst.
Other than that, I love the performance gain. Lipo to RC is like steroids in baseball maybe.. except lipo is gaining legal-ness in most places now.

Pete