I have designed two projects using Rastra and am a proponent of composite ICFs when used in the right climate.  The beauty of them is that you can stucco directly on the product.  One of  my projects was finished three years ago, and I have not seen a single crack in either the exterior stucco or interior plaster.  You can rarely say that about a stick framed building.

However, I am now replacing the foundation on my own home and looked a little further into the R-values of Rastra vs. other systems and concluded that Rastra was distorting its true R-values by adding a “thermal mass multiplier” which assumes the concrete core of the wall increases insulating performance. http://awesometesting.com/rastraold/therm_perf.htm  I have not been able to find a recognized independent testing laboratory that confirms Rastra’s claims, nor have I found a logical explanation of how this mass multiplier works. Oakridge testing laboratories compares straight R-values and you can see that there is no comparison between Rastra and Arxx.  http://www.ornl.gov/sci/roofs+walls/AWT/Ref/icf.htm  If someone out there can direct me to a source that can back up Rastras claims, I'd appreciate it.  Although that would mean that EPS only ICFs would probably have R-values in the 100s. 

I am not going to recommend Rastra or other similar composites for homes in my climate (Portland, OR).  I have not investigated autoclaved aerated concrete blocks and whether it has any advantages over composites like Rastra.  I'm now an enthusiastic proponent of expanded polystyrene only ICFs like Arxx.