How often do you take advantage of this?
Personally, I don't generally use them. I didn't even use the Event Torchic in X or Ash-Greninja in Moon (both of which are also non-native). I do make exceptions occasionally, though.
I don't mind evolving a native Pokemon into a non-native Pokemon, but that's only a thing in HGSS with evolutions such as Misdreavus -> Mismagius. In my first playthrough of HeartGold, I used a Leafeon.
I'm planning on using Milotic next time I play Y, so that'll be a non-native Pokemon. I can't think of any other times I've used them, though.
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Relax: bad things ringtone, best ringtones, zedge
Relax: bad things ringtone, best ringtones, zedge