No, CSPrimo Skin Changer uses Multi-Hack engines to avoid VAC security and performance loss. For this reason, it won't work without Main-Cheat. You must have Main-Cheat duration to use Skin Changer.
The security of Skin Changer is provided by Main-Cheat. Main-Cheat protects you against VAC-Ban risk. YES, it is 100% safe as your skins won't be visible in OverWatch.
One of the problems with the Skin Changer is during weapon changes, when you use the weapon for the first time, it may show a short fps drop.
For this reason, it is recommended to use it in Competitive and Casual mode, where you don't need to change a lot of weapons at the moment.
Skin Changer is not recommended until exiting the BETA stage as the weapons constantly change in modes such as Wargames and Deathmatch and there is a possibility that the opponent may be very close to you.