function looksSlower from LSR produces many warnings

[Marc Mouries]

I am using the function looksSlower from the snippet 
http://lsr.dsi.unimi.it/LSR/Item?id=305
and when i use it, it produces many warnings such as:
- warning: stem does not fit in beam
- warning: beam was started here

I tested the snippet and it does not produce those warning because it 
does not use custom beam

This function is very, very handy to learn music written with complex 
rhythm especially in 1/32 and 1/64 notes.

It is going to work with so many custom beams?

The function makes the music look 1 time slower. I was able to make it 
look 2 times slower by changing one of the number but I was wondering if 
is possible to pass the number as an argument?
looksTwoTimesSlower =
#(define-music-function (parser location music) (ly:music?)
  (let ((new-music (ly:music-deep-copy music)))
   (shift-duration-log new-music -2 0)
   new-music))

bwv-1001_1_new.ly
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