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Define "safe". Flashing and modding is safe as long as you know what you are dealing with. Read the instructions given by devs carefully before proceeding. Else, you'll be left with a bricked device. For cons, I think it would be better to discuss that in PE's XDA forums, not here. But it's a good AOSP based ROM, so you'll miss on a lot of MIUI goodies. Check XDA for more information.