A Holosun EPS Carry with solar and a green dot would be my choice for sure. I like the solar capabilities and I use it on my Shadow Systems 920CR. Get the C&H adapter plate for the EPS to mount it to your Hellcat. You'll barely be able to see the factory iron sights, so you may want to get higher ones. A Sig ROMEO-X or Vortex Defender-CCW will mount directly to the Hellcat without an adapter, allowing better cowitness with factory sights. Also Shield Sights (RMSc, RMS2, or SMSc): Since Springfield designed the Hellcat cut around the Shield footprint, these are a seamless, flush-fitting native choice.