Has anyone used Marvin's gliders. Historically gliders/sliders have a bad reputation, but these windows are claimed to have similar ratings as their casements. Being built for horizontal use vs. a double hung on their side they are said to have overcome the problems with sliding windows. This info comes from a marvin rep. Just looking for someone who has actual experience with these or opinions about them. My other choices would be Anderson's 400 series or eagles. Prices are almost identical to 400 casements & I am awaiting the eagle quote.