Yup. Many people have been caught out by it.
Claims for losses are limited to a stupidly low sum no matter how much you pay for the extra insurance for any musical instrument.
For smaller items like Class D heads, pedals etc, Royal Mail Special Delivery is a much better choice with better coverage options.
Or use an uninsured courier and buy a separate policy from Secursus. Although be aware they won't insure anything bought / sold via Ebay or reverb. Forums are fine though.