AssetManager will be used anyway. I prefer to use it for loading bundles, since I discover the problem with "yii" bundle loading.
The bundles config used by of "AssetController" is the same as for "AssetManager", so I think usage of the manager can increase the extendibility in the future.
Also, I can see no harm in "AssetManager" usage. Since "asset/compress" is a service command and will be run in backend and not often, the performance is not so critical.