Fire-4-Effect in El Paso TX did the milling on both of my Shadow 2’s. The first one was milled back in 2019 when the USPSA weight limit for Carry Optics was 45 oz, so F4E also did quite a bit of slide lightening cuts to get the overall weight + empty mag down to 44.1 oz. When I sent my second gun to F4E for milling in 2020 I requested the same cuts even though the weight limit had been bumped to 59 oz to have the two guns identical in feel.
IMO if you’re going to direct mill for the SRO or Holosun red dot, F4E offers a really good option bc in addition to the optic pocket they also mill a couple dovetails for inserts to make the slide slightly wider at the location of the mounting screws. If you look at some other company’s milling, part of the mounting screws are exposed due to the wider mounting footprint of the SRO/HS optic. For the Sig Romeo 3 and DPP the mounting holes are narrow enough the screws are not exposed.
I’ve been shooting my F4E milled Shadow 2’s since 2019/2020 with over 30K rnds on the first one and no issues.