I've looked at them, and HL sell a few. One from Nationwide has a yield of 6.25%, but I really don't know anything about them other than that they effectively seem to be a cross between shares and bonds.
Like bonds, the capital value is in inverse ratio to market interest rates, so it seems to be a reasonable time to buy them. The purchase/sell spread is about 2%.
I understand that in the case of Nationwide going bust, the owners would be last in the queue to get their money back.
Does anybody have information about these?