I don't know anything about the Mennards stuff, but from what you say, Redgard is nothing like it and a whole lot easier to apply. It's like a thick paint. You roll and brush it on, and when it turns bright red it's dry. Some people put on a second coat, rolling it on perpendicular to how they rolled the first coat. I did my 5-ft x 6-ft walkin shower in about 30 minutes.
I believe Redgard is a Home Depot brand. You might be able to order it from their website.