No, it will not and there is no way to mount a red dot to that handgun without completely modifying the slide.
No, it will not.
Because the Romeo 1 uses a proprietary footprint, it will not be compatible with the PDP. There are no aftermarket adapter plates that would allow you to install this optic. However, you can use the C&H Precision Weapons Optics Adapter Plate (linked below) and use that plate to install the Sig Romeo 1 PRO version, which uses the more common Deltapoint Pro footprint.
https://www.opticsplanet.com/c-h-precision-weapons-optics-adapter-plate-walther-defense-pdp-2-0.html?_iv_parent-gun-make=walther&_iv_gun-model=walther-pdp-2-dot-0&_iv_optic-cut=leupold-deltapoint-pro
It should mount using this adapter: https://www.opticsplanet.com/sig-sauer-sor11004.html?_iv_gun-model=239 however the lens will be very close to the ejection port.
The SIG SAUER Romeo 1 1x30mm Mini Reflex Sight will not fit the S&W Equalizer. Your Equalizer will fit any optic that uses the RMSc or K footprint such as the Sig Romeo Zero, Sig Romeo Zero Elite, Vortex Defender, Shield RMSc, Holosun 407K/507K, Holosun EPS Carry and more.
Sig does not specify where the Romeo 1 is manufactured. I would recommend contacting them directly for more information.
The SIG SAUER Romeo 1 1x30mm Mini Reflex Sight, 6 MOA Dot will not fit either of those handguns.
The SIG SAUER Romeo 1 1x30mm Mini Reflex Sight, 6 MOA Dot will not fit the Glock 43X MOS.
The SIG SAUER Romeo 1 1x30mm Mini Reflex Sight uses a proprietary footprint and is not compatible with the M18. You would need to use the Romeo 1 Pro model, which uses the Deltapoint Pro footprint, and can be found by using the link below:
https://www.opticsplanet.com/sig-sauer-romeo1pro-1x30mm-red-dot-sight.html
The Sig P320 Xcompact is compatible with the Sig Romeo 1 Pro at the link below. It will not fit the SIG SAUER Romeo 1.
https://www.opticsplanet.com/sig-sauer-romeo1pro-1x30mm-red-dot-sight.html