I am a professional structural engineer involved in condition assessment of existing buildings... that's what I do for a living. I have found Thermo-ply on several occasions and have walked away with the same impression each time, which is that this product has some problems. It appears to be an inexpensive solution to sheathing and must be used with caution. Here are a few specific reasons why I dislike the product:
1) It disintegrates rapidly and loses strength when exposed to water; this is not what is in the manufacturer's literature, but I've seen it first hand. If you imagine taking a cardboard box, even a strong box, and letting it get wet... well, we all know what happens to the cardboard, right? Well, this is no different. When this product gets wet it goes through very much the same physical changes that the cardboard box goes through. It warps, it swells, and it turns to mush! BE CAREFUL ABOUT HOW IT IS PROTECTED FROM MOISTURE DAMAGE (during storage on site, after installation but prior to siding, and how it is wrapped or flashed after installation).
2) It has very specific installation instructions that are often overlooked. First you must recognize that this product comes in three grades, or strengths if you will, that I am aware of. For an analogy, this would be similar to the relative differences between thicker sheets of plywood as far as strenght goes. The different grades can be easily distinguished by the color of the print on the sheet. Green print indicates the lowest grade (and is not really a structural sheathing), then red, then blue. Red and blue can be used (theoretically) as structural sheathing. So, be careful that you are getting the proper grade for the design of the structure. Second, the sheathing must be fastened in accordance with the panel manufacturer's instructions. I've seen this done well, but I've also seen this done poorly. It can be either stapled or nailed, but the installer must use the correct fasteners at the correct spacing.
3) My third observation is that it does not perform well as a substrate for siding. The manufacturer warns not to use it as a "nailing base", but I've seen it happen every time. As the siding is installed, it must be fastened to the studs, not the Thermo-ply. If you think you've seen bad siding jobs before, wait until you see one that has been installed using the Thermo-ply as the nailing base. MAKE SURE THAT THE SIDING IS FASTENED TO THE STUDS, NOT THE THERMO-PLY.