I've been using Arista drymount tissue for years.
The last batch I bought was distinctly different from early materials. Initially, it was a brownish glassine-like material. The newer version is a creamy white color and is much waxier. It is also perceptible thicker (sorry, I haven't actually measured the thickness).
Both new old and new versions have worked very well for me. The only negative comment is that the waxier new material tends to bead up just a bit when it is first tacked in place. I haven't noticed that this causes any visible bumps in the surface of the mounted print, but it is a bit disconcerting to feel irregularities in the dry mount tissue.
To John's point, I place the mounted print face down on a cool, flat counter top, and place a sheet of particleboard on top to weight it while it cools. A pizza stone would also work, but I would be concerned about getting mozzarella on the back of the print.