I've tried playing around with it, and this allows me to get the variant names that aren't in groups. Does anyone know how to tweak this so it takes the variant from a feature that's in a feature group?
Print our full array with features to get correct path
{$product.product_features|fn_print_r}
Awesome! I have realised by using this, that the Product Features information I need, is only available on the product page, if I check the box to "Show on the Features tab" of that feature. So that explains why I could find some and not others.