Do I still need Modern Sidearms?

No. As of update 2.6, Modern Sidearms has been merged into MF. Attempting to run MS alongside 2.6 or later updates will result in issues and potential crashes. We no longer support MS as standalone. Should you manage to find MS somewhere and install it, any issues you encounter using MS alongside 2.6 or any future updates are null and void, so please do not report them.