They add a quirky finish.
I didn't know she voiced those other characters;

On edit:
After reading the linked article, I see now this isn't about Helen Kane herself, but an impersonator..
Still, it reminded me how much I love to hear it.

This is a favorite, and certainly one of her most Boopish hits:

(voiced by Mae Questal) and lost:

Helen Kane lost her $250,000 Infringement Lawsuit against the creators of Betty Boop in court because she couldn't prove that her singing style, mannerisms and look was unique. Most flappers of the 1920s and 1930s, most notably Clara Bow, looked similar to Kane, she also was unable to prove that she originated the "Boop-Boop-a-Doop" scat singing, including the baby-talk singing style. In court it came out that a galaxy of singers had used "scat rhythm" before she did, and that the "baby-talk" singing style was a common method of singing, and that the "baby-talk" method of singing had been used since the early 1900s. In court it was proven that Helen Kane was not original, and that she had adapted her "scat singing" from other performers and or other performers had preceded her in that style.[1] Edward J. McGoldrick ruled in favor of the Fleischer Studios and Paramount Pictures after reviewing the evidence that was given in court. After losing the lawsuit, Kane appealed her case and continued to pursue the Betty Boop character, and was later told by another Judge, that being Judge Carew, that back then a voice, specially a voice that was not her own could not be copyrighted. You can also check out a scat-singing timeline here.
https://bettyboop.fandom.com/wiki/How_Did_Helen_Kane_Lose_Her_$250,000_Lawsuit%3F

Because of that, she probably wasn't paid as much as her peers like Rudy Vallee and movie stars like Clara Bow. The studio owned her and that might be why she couldn't afford to fight them.