They are absolutely worth the investment, especially if you live in an area with brutal winters, but the installation technique is everything. If you want a crew that truly understands the technical side of thermal efficiency and frame weighting, I highly recommend talking to the
windows professionals. They helped us select the right gas-filled options for our north-facing rooms and did an incredible job reinforcing the studs before securing the new heavy units. Our living room is noticeably warmer now, and we don't get any of that annoying condensation buildup along the bottom edges of the glass anymore.