Are static methods a bad pratice?

Question

Lets say I write a small wrapper for Android SharedPreferences :

public class ObjectSaver {
    private SharedPreferences sharedPreferences;
    private Gson gson;

    public ObjectSaver(Context context){
        sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
        gson = new Gson();
    }

    public void put(String key, Object o){
        sharedPreferences.edit()
                .putString(key, gson.toJson(o))
                .apply();
    }

    public <T> T get(String key, Class<T> type){
        return gson.fromJson(sharedPreferences.getString(key, null), type);
    }
}

I would use it like this :

ObjectSaver saver = new ObjectSaver(this);
saver.put("user", new User("Me"));
User me = saver.get("user", User.class);

Which is not bad, but I would need to initialize the class every time. (I know I can use Dagger but anyway)

To overcome this problem, I could set every method to be static :

public class ObjectSaver {
    private static SharedPreferences sharedPreferences;
    private static Gson gson;

    public static void init(Context context) {
        sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
        gson = new Gson();
    }

    public static void put(String key, Object o){
        sharedPreferences.edit()
                .putString(key, gson.toJson(o))
                .apply();
    }

    public static <T> T get(String key, Class<T> type){
        return gson.fromJson(sharedPreferences.getString(key, null), type);
    }
}

In that case I can initialize only one time :

public class MyApp extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        ObjectSaver.init(this);
    }
}

And then use it everywhere else like this :

ObjectSaver.put("user", new User("Me"));
User me = ObjectSaver.get("user", User.class);

This option seems actually pretty clean to me. My question is : is it a bad practice ? And Why ? (cause' I don't see this very often)

Thanks !