M3 Nova Default CT

Steam / v92+: Open the archive. Move the folder inside it (e.g. "skin_name") into: cstrike/custom/.

Old v34: Extract the folders (materials, models, sound) directly into your cstrike/ directory. Confirm "Yes" to replace all files.

Yes, fully compatible.
Mobile (Android): Install exactly like v92 (into custom folder).
ClientMod: Place the skin folder into cstrike_custom instead of `custom`.

Yes, they work on 99% of Community Servers. Only strict competitive servers with sv_pure 1 enabled might temporarily block custom models, but you won't get banned.

Your game might be running in low graphics mode. Open the console (~) and type:
mat_dxlevel 95
Press Enter. This forces High Quality textures rendering.

No, these are client-side mods. Only you see the custom skin. Other players will see standard weapons (or their own skins).