As I said in my answer Can antimatter be used as fuel for nuclear reactors? to your other question life is not that simple.
The estimate with neutrinos is for the free annihilation. If one wants to make a reactor out of this there are options to trap all charged particles before they decay and dissipate their kinetic energy in a medium, and ditto for all gammas from pi0 with ofcourse a different medium.
So, with an average of 5 pions per annihilation 2/3* 5*105MeV=350Mev cannot be recovered, the energy is lost in muon etc decays from charged pions when they become at rest( a bit can be gained from the muon track too). So the number of lost energy will be much less than 50% if the charged pions can be trapped and the energy of the pi0 photons converted to heat.
The problem is that with current technology one would need very strong magnetic fields to curl the charged pions. Calorimetry in high energy physics works by trapping all the energy of gammas, but these are large setups not designed for energy extraction as heat.
It is very probable that the cost of the technology needed to produce the antiprotons and create the magnetic fields to contain the charged products and capture the heat from the gammas will be much higher than the gain from the energy of annihilation no matter what the fraction. In my opinion the reactor cannot break even, i.e. give more energy than it eats up in its production, certainly not with the present technology.
So much for reactors. For explosions the energy loss in neutrinos holds, because the decays happen in flight and the energy is taken away by them. The technological problem is reduced to containing antimatter, and it is far from trivial, and I suspect equally cost/benefit negative as with a reactor.