1. A safer version of sys updater was released a few days after the exploit came out, that was much safer and made the chance of hard brick theoretically 0, assuming you don't do something stupid like install a FW from another region or 3DS model.
2. An even safer version of sys updater called SafeSysupdater was released that now checks if you have the right firmware before installation in case you can't follow simple instructions.
3. Downgrading from a firmware that is not 10.3 has a high risk of failing, and resulting in a soft brick that will force you to 10.5 to recover the 3ds. Me and a bunch of users had this problem when downgrading from 9.4 - 9.9. This wasn't a problem because we could just restore to 10.3 and downgrade successfully from there, but you're screwed.
Tl; dr There's always a risk of bricking when modifying ANY system, and you might be screwed because now because you were too scared to go through with it.