KF51's turret is not unmanned. The driver and extra crew sit in the hull, but the gunner and commander are in the turret.
The loader has been removed in exchange for an autoloader. But the autoloader can only carry 20 shells. It's just a Leopard with an autoloader. The new gun is a definitely improvement, but ammo is going to be a huge problem.
With heavy armour in the turret, it's as vulnerable to the T-14 as any other Western tank. It's only an improved third gen design. Basically, while APFSDS is largely useless against the T-14's turret, the T-14 can still use its APFSDS effectively against the KF51, so that's a major disadvantage.
This tank is a decent option for new users of Western tanks who are in the market for a new tank. Current users should just upgrade their existing Leopards and wait for the Franco-German MGCS to deliver. This new tank does not provide any significant advantage due to the weakness of the turret over the T-14.
Anyway I think this tank was made as both a demonstrator and as a competitor to the South Korean K2 that's making waves in Eastern Europe. The K2 has a much lower profile than Western tanks, so that gives it a pretty good advantage against the Russians. With Eastern Europe interested in getting rid of old Soviet junk, and with the Polish going for the K2 and K3, the South Koreans have a massive advantage over the Germans, and the Leopard wouldn't cut it. Nevertheless, I'd say the Leo 2A7 has a greater advantage over the KF51 in Eastern Europe. So, unless Germany invests in the tank, I fear it will remain a TD.