Most have less preferred than leverage. So you might be getting 110% equity REITs and 23% preferreds with 33% leverage. (Not speaking specificly of NRO, but in general.) I believe they are limited to 150%, and so most use around 133%, and most of them have a 80/20 equity/preferred ration in their prospectus. When you take the leverage into account, it probably is a good thing they lock in some fixed income with the preferreds to pay the interest on the leverage.
NRO is an interesting one. It had an activist investor in it that recently forced it to merge with NRI. That's not nesicarily bad, because it makes a bigger fund with more liquidity. However, it the activist investor also got them to adopt a payout policy that anticipates gains and pays them out as part of the regular dividend, where as a lot of the other CEFs pay the gains in a special dividend at the end of the year. So, this seems to me to make it more likely that NRO could at some point cut it's dividend. I'm not saying that they would, I'm just saying that where other REIT CEFs might just pay lower gains at the end of the year, if NRO was faced with the same situation it would probably end up cutting the regular dividend.
Others to look at might be RPF, SRQ, and JRS. IIA is another but it has a bit higher ratio of preferreds. (Cohen and Steers also has one that does not use leverage - RFI.)
Since these are actively managed, they may have slightly different strategies. So by diversifying across multiple of them, you may avoid ending up with just one that makes a bad strategical move.
There are also a some international ones: RWF, IGR, AWP. (AWP doesn't use leverage, but instead uses dividend rotation to enhance the yield.)