Hello,
Thank you for the detail included in your description. I have had a brief look at the Sweet Home 3D program and am currently downloading the MyFourWalls to look over as well. This project seems very similar to what I currently do in my day job. I will usually bring in target customers to test a product as well, but am very well practiced at completing expert usability reviews.
I can spot things that others may not anticipate to be usability issues and am extremely thorough in my assessment of a product/website.
I can provide you with the exact information you need to determine which product is more usable and therefore will draw more customer retention.