A clear upgrade on standard shakers with an easy to clean base; no residue, or worrying about drying the shaker completely before putting your protein in it. Mixes surprisingly well, without a metal ball. No issues to report. Problems start with the outer matt rubber coating: I only use cold tap water to rinse my shaker, and it stays in the kitchen, but it is now peeling away. The sliding lid mechanism is too stiff according to some reviews. I have the opposite problem with the sliding lid being too loose, with it closing as I lift the shaker to drink. It either slides against my upper lip, or partially closes the spout, leading to a mess. Very frustrating, but can easily be fixed with future iterations.