AFAIK (which probably isn't that far) it's not any worse if you die from the explosion, but, unlike with a regular bomb, with these if you survived the blast you have to then immediately find air to breathe (probably while injured) because they're designed such that they consume all the oxygen in the immediate vicinity. So even if you're already outside, unless there's a stiff breeze you might not be able to crawl to where there's breathable air before you die.

FTA: Another Defense Intelligence Agency document speculates that, because the "shock and pressure waves cause minimal damage to brain tissue ... it is possible that victims of FAEs are not rendered unconscious by the blast, but instead suffer for several seconds or minutes while they suffocate".

The Russian military has already used at least one in Ukraine in recent days. I submitted a link to a video the other day, but it got flagged. https://news.ycombinator.com/item?id=30494506