I do a lot or roofing; I have done a lot of quality compliance
inspections for different companies. I am in S. Texas, which has the
same high UV days as well as high heat and humidity.
I am also familiar with a lot of different coatings and applications
that "extend" the life of the roof.
In a word, baloney. In two words, no way.
ANY clear coating of any kind that you expose to that kind of
punishment (18 hours of sun and heat a day) will fail. Polymers are
either resins or plastics, and they will sit on top of the roofing
material. You will never get the roofing material clean enough to
provide any kind of seal at the time of application. Even if it
appears to penetrate at some demo, it is probably just the carrier or
solvent going into the surface.
More bad news. All the roofing products we use around here (excluding
tile and metal) use petroleum products in their manufacture. They off
gas vapors for years, until they are dried out and crispy. So, you
will have petroleum vapors off gassing under your plastic finish.
Think of the coating as an instant green house.
And when it starts to fail, water will seep in under your poly film and
begin to mold and mildew. Then the finish will start to flake off.
Think of a varnish covered front door that hasn't had any finish
applied in many years.
But then, they may try to sell you a renewal material for future
application. That makes it even worse. All poly finishes are film
finishes and will not "renew".
You BEST bet is to have your roof installed correctly, and if you are
in doubt about them blowing off have the roofers put a couple of extra
nails per shingle, and make sure the nails are in the 1 /14" range when
the roof is installed. Sometimes a shot of mastic will help ridges and
hips in addition to the nailing required.