It's a bit like the the body with vitamins. At first they thought vitamins were all you needed - then they started discovering micro-nutrients.
Blood is pretty complex - does this include just the highest-order bits of blood, or does it include everything that blood has?
Once back in a hospital setting they could switch to using real blood.
1 - Volume - You need enough fluid in a closed system to maintain pressure to push that fluid.
2. Oxygen carrying capacity - Oxygen binds with red blood cells which then deliver it to every cell in your body.
Right now the prehospital setting can more or less manage #1, we have been for a century with Normal Saline.
There is some stuff circulating (pun intended) regarding fluids that can transport oxygen but it will be years before we can use it
So the question is whether it works in emergency situations, not whether it is as good as the real thing in all ways.