Since all the lifegain is only one instance, you have to deal all the 104 damage to a single target/player, leaving all your other opponents completely fine.
And then you have this giant target painted on your face because you are now the guy with …
I think using Brightflame instead of BA+ Hallow would be even more useful in some environments, i.e. EDH. While it would cost a fuckton more mana to get the same amount of Damage/Life, you actually get to destroy your opponents' creatures.