I bought 5 of the Bushnell TRS-25's when I found them on sale for $55 with free shipping. Bushnell had a $40 rebate on them at the time, with a maximum of 5.

For $15, they've been great.

For Steel Challenge, I run a C-More RTS-2 on my Black Mamba and a C-More Railway on my Volquartsen Ultra-Lite.

I'm also a big fan of the Holosun 507C and 510G.

There's never been a better time for red / green dots!