I think that I can be of help with this one. First, let me say that we have been homeschooling for 10 years and this is the first time I have ever "ditched" a curriculum mid-year. I had such high hopes for this program and I am really disappointed.
Here are my opinions:
1) The IG is very poor. The way that the experiments are scheduled to be completed (often over several days) conflicts with how they are set up in the KOSMOS guide. For example, KOSMOS will run similar experiments under the same conditions in order to compare results. Unfortunately, it looks as if WP didn't really read these through before creating the schedule...it's not possible to compare the results accurately if they are not done one immediately after the other.
2) The Power House kit often had extremely poor directions and several times, I called in my husband (who builds models and is extremely inclined in this area) to help us with assembly. NONE OF US could figure it out. Unfortunately, this happened more than once.
3) The activities in the student book seemed very disjointed and often seemed like "busy work"--very time-consuming "busy work".
4) Alot of the time, I was not even sure what we were supposed to be gaining from an experiment and there was no place where the information was really explained well, I found myself on the internet searching for supplementary explanations, videos, etc.
5) This program was advertised as "open and go". For our family, this was definitely not the case. I spent so much time trying to reorganized the IG to help it make more sense. Also, I was not aware that so many of these experiments would have to be completed outside--we live in the Northeast--not likely that we will be using our solar cooker in February-Again, this meant moving things around.
I hope that this assists you in making a decision--for us, this was a huge, expensive mistake.