Substrtate heating

Has anyone tried FlexWatt mylar sheeting for substrate heating?
The better reptile shops have used it for years and it is really
easy to work with. 

Some of the large stores like Menards carry it in 25 to 50 ft rolls 
for bathroom floor heating.  The rolls are divided into 12" sections
each being 10watts.  The rolls are about 14" wide and will work for
40gal and larger aquariums.  For a 75gal, I cut 36" from the
roll giving me a 30 watt heater spread evenly under the tank.  It is
laying on 3/4" plywood under the tank and I can feel the increase in
temperature on the bottom of the plywood.  It is wired to a rheostat
so it can be turned off and on and adjusted as well.

I had never been able to get Echinodorus species to really flourish until
I installed this heater.  Now they fill the tanks beautifully.  What I
really like is the ease of installation, the safety of outside-tank heating,
and the even spread of the heating under the tank.  I have since installed
this system on several tanks with equally great results.

I had been critical of the need for substrate heating, but I have seen a
real difference in plant growth since I've started using it.

With the proliferation of reptiles as pets, I had thought I would see a post
about this in this list by now.  

I have been trying to think of things I would regard as drawbacks  as
I posted this, but I'll be darned if I can think of any. 

Is anyone using this method?

KArl R. Schoeler