Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now
4 of 6 added 69 characters in body

Jelly, 13 12 bytes

-1 byte thanks to @Luis Mendo (use to replace %2)

Œlf“aeiou”LḂ

All test cases are at TryItOnline

How?

Œlf“aeiou”LḂ - Main link takes an argument - s
Œl           - lowercase(s)
   “aeiou”   - string of lowercase vowels
  f          - filter - keep only the vowels
          L  - length - the number of vowels
           Ḃ - Bit (modulo 2)

Non-competing, 5 bytes (since I just added the function Øc)

fØcLḂ

Test cases also at TryItOnline

Same as above, but Øc yields the English vowels, 'AEIOUaeiou'