5% return is incredibly low for this security. Some governments issue perpetual bonds at rates higher than this. The US and UK also both issue 20-30 year securities at rates around 5% (and when you factor in that you get your principal back, it's basically the same).
The 5% is for the whole 20 years though, not on an annualized basis. You can redeem these after 1 year.
You're right, this investment
is extremely low-risk -- suitable to dump $1M+ into without thinking. This is a real investment for serious money, not a $1200 rig or dipping your toe in with a couple of BTC riding on just-dice profits.
You can do that with bitcoin too, but you risk losing 50% just as much as you risk a gain. I know lots of ppl who were selling in the 900's, then the 800s, then under 800, because they
knew. Just saying. And that was, like, 1 or 2 months ago.