Thank you for the info, Steve. The "Features" confused me because the product page appeared to pick up on product variations, which is what were all coming out N/A. I deleted all the variations and tried to enter them in as Features but they rejected as "already present". I had to go into the database and directly delete them from the compare_fields table then they could be added back in.
BTW, what's with all the BLOB types?
About the Compare button not showing on a single product page, this happens regardless of the before/after setting when the "Add to cart" button is disabled, i.e:
The plugin doc does provide template code to get around this, but doesn't offer any help on which template to insert it. After some hunt and peck around the WooCommerce plugin files I did find an action hook that did a satisfactory job. BTW, the only way I found to hide the Add to Cart button in the compare pop-up was to set display:none in the stylesheet. It would be preferable to disable this with an action hook, too.
So all is figured out now and I can better appreciate this plugin. Nice job :)