Their share prices fluctuate in a very narrow range. You are getting more bond for your dollar if you by them at a discount. They are not widely followed and researched by brokers. As always, they can fall to an even bigger discount than when you bought them. If there is a large number of defaults in the bond portfolio, your share price will fall.
Some funds borrow heavily to increase their bond holdings.
This leveraged buying makes the fund more volatile. They offer a monthly newsletter called The Investor's Guide to Closed-End Funds . Barron's Online Barron's carries useful information on closed-end bond funds in the Market Week and Fund Column sections of it's website and weekly print edition.