Tenax is actually Methylene Chloride rather than MEK (according to my "sniff test" since Tenax doesn't reveal the ingredients in the bottle). Methylene Chloride is a water-thin solvent used extensively in making invisible welds in Acrylic and Lexan plastic (Like when making clear display cases).
MEK and Tenax are definitely two different solvents, and I did not intend to imply they are one and the same. I actually prefer the MEK, it seems to have better "melting" power and less viscosity than Tenax, which makes it useful when working in highly detailed areas...e.g. splicing hood doors in a shell.