I put Solexx up on my endwalls a year and a half ago. For 20 something year prior to that, the endwalls were just single layer poly. While the Solexx is a much stronger material which I appreciate, there are some definite considerations to take into effect. First, it expands and contracts like crazy making it virtually impossible to seal completely. With poly, while it might have slight expansion/contraction, the wire lock keeps it sealed tightly all around the perimeter so no openings for pests or varmints(mice, frogs, snakes, lizards to name a few that have gotten in since I put the Solexx up!) The cost is considerably higher than poly. While it lasts much longer and is not damaged by high winds and flying debris, you can replace poly many times over for less money. Solexx is considerably darker than clear poly. I see a big difference in transmitted light on my South endwall. Don't really care on the North side but I keep my lettuce and basil starts on a table at the South end and they definitely grow slower now with the Solexx up than they did with clear poly.
I have built over an acre of commercial greenhouse space in SW Washington over the last 25 years and I can absolutely tell you that I would never use Solexx as a cover. I can deal with problems it causes on the endwalls but there is no way in hell you would ever get the seams to stay together as a main cover. I can only imagine all the leaks as well as bug problems it would create. While I would love to find a longer lasting, more durable cover than poly, it still provides the best ROI and suitability in this part of the country.