Old thread but I'll throw in my 2cp.
The way it seems to read now, it gives you +1/level. The +3 makes it a bit more useful for the 1st-3rd level characters since it gives them the 1st 3 levels worth up front.
It doesn't matter when you take it (which is the clarification I was trying to wrap my head around). If you take it at 1st level, at level 5 you will have +5 HP from it. If you take it at 5th level, it will give you +5 HP.