In a past life, I was an industrial roofer and these do seem like a good idea until you need to fix the roof. If you start with a metal roof, this wouldn't be a problem I believe. But if you are using a mod-bit roof, a rubber roof,or even for some reason an asphalt roof, the roof at some point will need to be replaced or fixed.
It is also to my understanding that the flexible, roll-on PV panel has fewer Watts per square inch than the ridged type, so you will need a larger area for the same wattage.
I know nothing about the durability of these PV units, but it seems to me that they would be more vulnerable to the elements than standard ridged units.
Another up side to ridged units is the ability to take them down and with you if you should ever want to. If things ever got a little hairy and you could get them out of town, ridged panels would be worth a gold mine. The stick and stays, well, they would stay right there.
Another consideration came to me... It is to my understanding that when a PV panel heats up too much, wattage decreases significantly. Ridged panels are set up so there is an air gap between them and the roof so that air can move and cool them. Having the panels applied directly to your roof defeats this purpose, so in my mind, you run the risk of over heating your panels during the summer months and decreasing your output. A roof is a hot place to be on a summer day, even on a white painted roof.
Just a few thoughts. If some one could correct me if I am wrong, please do. These are just a few of my thoughts and opinions.
Well the consideration i would make in that situation would fall only on how durable the flexible panels are. And to answer that you need to remember there are 3 common types of solar cell for power generation (and a good number more used for other applications that I'm not getting into) First the best type is monocristalline. There the cell is made from a single cristal of P or N type material and doped with either N or P type material depending on what type of material the cristal is made from in the first place. This is the best type of panel there is available to the common person. The second best is the polycrystalline type. basically the same as a mono but there made with several shards of material glued together to make the cell. In practice there every bit as good as there higher priced cousen and just as durable. The trade off comes where there not quite as good at converting sun light to energy, but they make up for it since you can make the cells square or rectangular and therefore have more cell in a given square foot. And in practice since you end up with more cell surface working for you they end up dead even in performance and cost slightly less. Both the above cells should last 30 or more years if used every day. Now the last type that is avalible to the common home owner or other person seeking a solar panel is the amorphous cell. The only advantage of a amorphous cell is there cheep and come as both rigid cells and as flexible cells depending on the substrate there made on. There bad points are they tend to run at a lower voltage and they don't last as long. 10 years is about average for one in every day use as far as my experience goes. That said they don't tend to just quit working all at once. They just start making less and less power as they age. But the test data i have seen on them tells me there almost useless by the time there 20 Years old. And if there out in the sun where solar panels tend to be that aging will happen faster.
Now i will admit its been about 5 years since i have done my homework. The technology gets better every day. But the real deciding factor is how long the manufacture guarantees the panels rated power. If there still only giving 5 or 10 year warenties on amorphous cells then what i just said above is still likely true.