In my opinion, the SIG Romeo-M17 red dot is a really good piece of gear, but substantially overpriced. This is a red dot that SIG has developed specifically for the M17 and M18 military pistols, and is not compatible with any other platform. By using a proprietary mounting setup, SIG is able to make this a very low-profile optic compared to other closed-emitted red dots, and it fits the lines of the gun very well (less of the mailbox effect than one normally gets). The controls are good, and the optic gives you the choice of a 2 MOA dot, 32 MOA circle, or both. The battery (CR 2032) is side mounted and easy to change. The lens has a blueish tint that I would prefer not to see, but it doesn't seem to actually cause any problems for me.

Really, the only downside is the substantial $800 price tag. Of course, if you are a military customer you have no real choice...and so if you want to duplicate a military M17 or M18, you'll have to pony up the moolah for a Romeo-M17. At least you will have a really good optic when you do, though. If you don't need to have the military item, you can get an adapter plate and mount one of the other much less expensive commercial optics on your P320/M17/M18.

Full disclosure: SIG sent me this Romeo-M17 free of charge.