We ordered 4 Indow Window inserts to see how they worked on our steel casement windows. We are very pleased with the fit and finish, and especially the improvement in wintertime comfort. Steel casements present challenging issues when trying to improve efficiency. The only downside for our installation is it required the removal of the locking and operating hardware to work in concert with our window treatments. The attached photo is during installation with Indow inserts installed on the two left pair; not yet installed on the two right pair. Pretty minimal visual difference! I'm now ordering 17 more inserts for the rest of the house.