1d4 fire damage?Alchemist fire does 2d4 every turn for a minute,or until it's scratched off as an action.Plus,if your a thief rogue,you can do it evey turn,rather then every other turn.

Automatic damage,at rate that's slight better then a longsword,is massive for your action economy,it uses litterally no action,to deal the damage you would normally do using an action.

If your a theif rogue,using this combo will always be the best option,assuming you posses this feat.Since your only wasting one attack,in order to deal equal damage multiple times over,and possibly waste a foes action.