The only major difference is the mounting pattern. The Rome1Pro was made specifically for the M17 pattern handguns to match military specifications.
Difference between the SIG Romeo 1 and Romeo 1 PRO:
The Romeo 1 PRO
• The mounting pattern is different – The Pro is made to mount on the M17 and has the same mounting pattern as a Delta Point Pro (DPP). So again, the new Romeo1PRO will NOT fit old Romeo1 mounts or slide cuts. The Romeo1PRO is meant specifically for the M17 cut slides and matches the Leupold Delta Point Pro red dot footprint. The PRO is more designed to fit the P320 compact
• the battery lasts longer (2 Years or 20,000 hours) but one should change the battery annually or more if you use your gun regularly.
• It comes with a shroud around the optic (Protective Shield). The Romeo 1 does NOT come with the protective shroud
• It has a better dust cover.
• It has a brighter dot
• On the PRO, the dot can go from dim to bright in 12 steps. The non-Pro goes from dim to bright.
• It is important to clarify that there are two different Romeo1 PRO models:
1. The Romeo1 PRO which is supposed to use the Leupold DPP footprint
2. And the Romeo1 T which is supposed to be the same improved /Gen3 sight with the proprietary Romeo footprint.
The mounting pattern is different, the battery lasts longer, it comes with a shroud around the optic, and it has a better dust cover.
It is also made for the foot print of a P320 x compact. Along with the Delta point Pro made by Leopold.
The Romeo 1 Pro has the protective shield included and brighter dot.