The part that made this whole thing frustrating was the readme in the main folder of the unzipped file:

INSTALLATION:

See the install text depending on what version you are installing:

install.txt
upgrade.txt
uninstall.txt
This should be made more clear, since it is NOT the correct directions for 1.5.0.

And the bit you just quoted is for upgrading ZEN CART from 1.3x to 1.5.0, right? If not it's confusingly worded. I've never used ZC 1.3.x; I started out my whole Zen Cart odyssey with ZC 1.5.0--so in my case, what file do I run? If this is the one I'm supposed to run it's badly named: install_testimonials_manager new_install.sql since this is not a new install--I already have Testimonial Manager installed. On 1.5.0.

Actually, I can't even find that file anywhere. I found a 1.3.x_Upgrade.sql (which sounds wrong since I'm not, and never have been, on 1.3.x) and new_install.sql (which sounds wrong, since it's not a new install). So the instructions are not clear at ALL about how to upggrade Testimonial Manager under a ZC 1.5.0 installation. The directions in the 1.3.9 folder may be clearer, but they don't apply to me so that doesn't matter much.