Gladys,
 
I have both the Silvergen and Silverpuppy, as well as other machines.
 
The silverpuppy automatically stops at 16 ppm for me.  Some get 20ppm.  I have  
no problem with this at all and i use this all the time.  I got the convertible 
120/220 so i can use it anywhere.  This machine  stops if the distilled water 
has excess minerals or not too pure. This machine does not make a lot of the 
fuzzy silver fibers on the electrodes.  This has two kinds of magnets stirring 
the water, but you only choose one to use.  I also get good technical support 
from Ken.
 
The Silvergen, it has a dial, and if i use the lowest setting it only goes up 
to 2ppm.  Then if i put it at the 12 o'clock placement, it would give me 4ppm.  
Then i put it at the 3 o'clock setting it would give me 5ppm.  Now, one can't 
turn the dial to the max coz that would break the machine.  Like the 
silverpuppy, it gives a clear solution as long as you truly have a good 
distilled water.
This machine automatically stops when distilled water is not too pure.  It also 
stops when it has reached your desired ppm. It also does not have too much fuzz 
on the electrodes.  You don't push the stirrer too far down otherwise it would 
not turn.
 
Those are my two cents on my personal experience with the machines.
 
Melly