GE R.O. Water Filter

[Pat <pat@xxxxxxxxx>]

I installed 3 of the subject GE reverse osmosis water filters about a
year ago.  (The model number is PXRQ15RBL).  My daughter wanted one
(because she didn't like Los Angeles city water), so I stalled one at
her place.  I liked the way it installed easily, so when I returned to
my Ohio well water, I installed an identical model here.  Our well
water wasn't bad.  There was an occassional slight sulfer odor, but
testing indicated no harmful bacteria.  It is also softened.)  The
filter seemed to work well, but I found myself also drinking water
from a bar sink in the basement family room.  This seemed silly since
I had installed the filter upstairs - so I bought another filter and
installed it at the basement bar sink.  That's it for background - now
to my question:

The manual says to replace the "pre" and "post" filter canisters every
6 months.  To make the product seem high tech, they even provide a 6
month timer that lights an LED when the 6 months is up.  That is all
it is - a timer.  It does not measure usage, flow rate, or
contaminates at all.  So, how often do I really need to change the
canisters?  The filter installed upstairs is used for making coffee,
tea, and meals every day, while the filter at the bar sink is used for
only a few ounces of water no more often than once a week.

I can't imagine why both units need to have their filters changed at
the same time.  Do the filters get clogged?  (Mine haven't even on the
higher use sink).  Do the filters become contaminated with bacteria?
In that case, the lower use one might be worse.  (In my case, there
have been no foul odors nor reduced flow).  Both LED indicators went
on at 6 months and blinked until the batteries died.  I just can't see
spending $80 every 6 months for no reason.  Does anyone have any
inside information or real experience regarding these things?  How can
I tell when they really need to be changed?  Am I being reasonably
frugal or risking my life?

Pat