What the f*ck? No, wahkao, that's not even remotely right.
I'm gonna step in here before this goes even further off into wrongness.
Mortgage REITs are a uniquely American thing. To understand how they work, though, you have to start right down the bottom of the stack with the American mortgage market.
American mortgages are a bit odd. The vast majority of them are 30-year
fixed-rate mortgages, and if you're thinking "wow that's an awesome deal", you're right. The mortgages are issued by banks, insured by Fannie Mae or Freddie Mac, and then packaged up into "mortgage-backed securities", which is just a fancy way of saying "bonds backed by people's mortgages". This mortgage bond market is huge in America - the MBSes offer a somewhat higher yield than regular US government bonds, with minimal credit risk (because they're implicitly backed by the US government through Fannie and Freddie).
(The tradeoff for the higher yield is that you've got a thing called "prepayment risk", which basically means "if interest rates go down, people will refinance their homes, so your mortgage bond matures early and you have to reinvest the cash at the lower prevailing interest rates; if interest rates go up, people won't refinance, so you're stuck in a bond that yields a lower-than-market interest rate". So if you buy mortgage bonds, you're effectively short interest rate volatility, and that option can be priced and hedged like any other option. Prepayment risk is a fascinating quirk of the mortgage-bond market, and I'd love to put in a discussion of it here, but
this margin is too narrow to contain it. (Incidentally does anyone else think Fermat was just epically trolling us with that note?))
So that's MBSes. Where mortgage REITs (henceforth mREITs) come into this is that they're a uniquely American spin on the regular REIT structure.
The American rules on REITs are similar to Singapore: you get a tax break as long as you pay out all your net income as dividends (or something like that). But American REITs can hold MBSes as well as actual real estate, and that's what mREITs do.
They leverage up (borrowing money from their banks at low short-term rates) and buy MBSes using anywhere from 2x to about 8x (!!!) leverage. So instead of just getting the 3-ish percent you'd get on a current-coupon mortgage bond, you get that multiplied by 2, or 3, or a lot more than 3. You get the real-estate exposure of a leveraged REIT, without all of that messy business of owning actual buildings.
The tradeoffs, though:
1) Volatility. Owning a many-times-leveraged bond portfolio is a recipe for volatility in your share price.
2) Interest rate sensitivity. mREITs lose money when short-term interest rates go up (because they have to pay higher rates for their leverage funding), when long-term interest rates go down (because their portfolios get prepaid), and when long-term interest rates go up (because they're stuck with mortgages that are at below-market interest rates). Interest rate volatility of any form is bad for mREITs.
There are some things that mREITs are not:
1) They are not ABS-CDOs. Mortgage backed securities are not CDOs, and neither are mREITs. (Though that said, there's some vague similarities if the REIT issues debt as well as equity.)
2) mREITs almost never own CDOs. This was a thing back in '06 (a lot of CDOs were issued that were backed by the preferred stock of mREITs, which is just a leverage nightmare), but it's really not a thing any more.