Looks like you like golf :D

errrr.... it's actually a good question... x)
3 years later, I'd actually say it's perfectly fine in this situation (I guess I had in mind something about saturation of the memory with the extra list, but in most situations you won't see any problem. Now, if n is huge, you'll run into troubles anyway, but not necessarily because of the approach itself, but rather because of the size of the string you have to build...)

ccl: forget that message.

Could you elaborate on which specific aspect of the above code is dangerous or footgun-y?