One of the best design evaluation methods I found was to teach and train others on the products. Occasionally doing onsite project installations was a good feedback loop. I wouldn't let them know I was a principal designer. Would sit back and see how well they grasped the design and constantly take notes on how to improve it.

I want criticism about the designs. Tell me where you think the product is junk and why. There is not one user but many users you are designing for in a single product. Each has an unique take and requirements. Features to sell it, those that write the checks, and those that use it daily must both be met.