Debentures where we sat

To read Australian Securities and Investments Commission site, debentures are a risky proposition. There's an Accounting Management blog that categorises them in similar fashion to other forms of investment yet the emphasis on unsecured and the like, and talk of a pecking order in debentures that get paid (not to mention non-redeemable debentures that only get paid when the company goes into liquidation!)  hardly warms me to them.

eFinance Management tells us  'The debenture classification is based on their tenure, redemption, mode of redemption, convertibility, security, transferability, type of interest rate, coupon rate, etc.'

Redeemable Debentures
Irredeemable (Perpetual) Debentures

Convertible and Non-Convertible Debentures
Fully and Partly Convertible Debentures

Secured (Mortgage) Debentures
Unsecured (Naked) Debentures
First Mortgage Debentures
Second Mortgage Debentures

Registered Debentures
Unregistered (Bearer) Debentures

Fixed Rate Debentures
Floating Rate Debentures

Zero Coupon Debentures
Specific Rate Debentures
Secured Premium Notes/Debentures

Callable Debentures/Bonds
Puttable Debentures/Bonds

Perhaps there's not that much difference, though the focus is on 'debt instruments'