Pros:

+ Works just fine.
+ It's Nyan Cat. :l

Cons:

- Not sure if this is just me but when others heal me it's barely heard. 
- About the volume comment-- I'm sure that's easily adjustable through the audio settings ingame and elsewhere.
- For me (and personally me: when I play with my friends and others online), I can see it become annoying as my friends constantly 'joke heal' (i.e. letting the bar fill the stop and do it over again) but heh, that's just me. No points off on that.

Conclusion:

Tested it with low and high game volume both headphones on and off. Works just fine for me and it adds a bit more silliness to my games. Something that I enjoy. What I also really enjoy is how it cuts in and out at the right time.