I like the metal particles sand sword. To me, it requires a lot more control than what we've seen from Mikoto so far, so it was a nice addition. Now I understand a little more why she was a relevant target for the Accelerator.

I also think Touma is a great sparing partner for her.
He's the only one with who she be at full power. Being able to use her power at will is a big plus towards controling it even further. It might also be good for stamina.
We know little about where the energy comes from for the various powers and if overusing them could cause some kind of depletion.