I guess we all get:
Fatal error: Call to undefined method yclass::init_template() in /zentest/admin/module_manager.php on line 14

If we follow instructions and install Module Manager first and then
the Cross-Sell mod after.

Yellow: Could this be fixed in the modules in download? Or at least edit the intro text to clearly state this problem? Costs everybody some nerves, shock and time to search for the solution. Never great to have errors on your screen when you try a new mod.

One more time the solution is:

substitute the file(from the cross sell):
"<zen-cart-root>/admin/includes/init_includes/init_yclass.php"

with the version from (moduls manager):
<zen-cart-root>/includes/init_includes/

Works great now. Thank you for another great mod.