Testing version 1.0 ... Two problems so far:

1) Line 216 $kit_test = db_query(); "Missing argument 1 for db_query()"
2) You never check to see whether the Product Kits module is installed. When it isn't, there are a lot of DB errors since you're making queries against uc_product_kits regardless.

Have you tested this code with product classes?

Can you remove the drupal_set_message() calls, or maybe add "debug" checkbox to the admin menu to turn these on only when wanted?