I've been trying this for the past day with little results, but not too hopeful.
I bought a copy of FE Echoes, used. Sat on my shelf for 6 months before giving it a try, and got the "game cart could not be read". Tried cleaning it, nothing. One time it ran, but got stuck on the 3DS logo.
I then ran the 1.0 fixer, got from 0 to 1% and then stuck there. Cancelled, tried again, same thing. One thing I noticed is that before, not even the splash screen was showing, before selecting the icon in the home menu. After that, it showed up, but still not running.
Then I tried the 1.2 version. Everytime it asked to skip a block with Y, I did it, and almost everytime, it went up by a %. Around 80%, it rushed through to almost a 100%, when I skipped again a couple of times and it finished while I was away, and apparently restarted. I got back home with it around 15% again, stuck asking for a skip. I did that, it went slowly towards 100%, then completed. It asked to verifiy, which I tried, but didn't work. I then tried loading the cart from the home menu, and it did, but crashed during the opening cutscene. Tried again, managed to start a new game, but it crashed in the 1st cutscene.
When I decided to try the 100x version, something went wrong with the USB, and I had to reinstall homebrew, godmode, etc. Now I finished that, and tried both the 100x version and the 1.2, and both of them stopped at 1%, just as it was yesterday when I tried the 1.0 version.
I'm letting it run now, but I'm not confident that I'll be able to salvage it.