That is true because when I send bitcoins and set the right amount of fee it's not that accurate. The fees can be way off for example you put 200sat/byte fee then when it's sent you'll see that it's 170sat/byte. Blockchain doesn't have high security you can find an article about blockchain giving refunds to those who got hacked few years ago. The old/legacy version was better than this. They support three coins now including bitcoin cash.