I run a 5.11 Tactec plate carrier for Airsoft and use it for fitness with Beaver Fit plates (14lbs). It is incredibly well built and holds the plates fantastically. It’s designed to hold SAPI plates and a number of Police forces ARVOs are issued with them and wear them daily. They aren’t cheap though but you get what you pay for.
Not sure abou the fit for Osprey but trust me you want the plates fitted in tight or you won’t enjoy it!
Warrior UK make some real steal plate carriers that are cheaper and will also take SAPI plates as do Pentagon, Condor, LBT, Ferro Concepts and a host of others.
Just stay away from brands like Viper, Nuprol, Emerson and One Tigris. They are ok for Airsoft but I wouldn’t trust them with heavy plates as they are not milspec.
From my experience if you are choosing a plate carrier to run SAPI or fitness weight plates I would advise this;
Ensure there is good padding on the shoulder straps as this is the first area to ache.
That their is sufficient padding body side of the plates. If the carrier moves around inside the carrier when you run it will get real old, real quick.
And make sure the chest cumberband has some elasticity to allow your chest to move when you start breathing deeply. The trick is to do it tight enough for it to hold still but loose enough to allow you to breathe.
And in case you missed it here is a review I did of the TacTec.
Hope that helps.
CBH