I bought the string Beylauncher LR because I have a preference for string launchers and because on the back of the packaging it says that the power level of it is 4 stars, compared to the light version which comes with Legend Spriggan which is only 2 stars. 

It seemed pretty strong and allowed me to reach 1,040 Rpm max according to the beylogger/app. 

Today however I received my Legend Spriggan and the light launcher LR and after using it a couple of times my top speed on the app is now 1,500...

Is my string launcher faulty? Or were the power level stars on the packet a lie?

It doesn't really matter, those numbers are pretty exaggerated by TT, your string launcher is completely fine

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Beyblade Burst is cool, I once made a continuation of MFB, but I stopped, but now I've restarted (Then stopped again). Geist Fafnir is also pretty cool

MR System Beyblade: https://worldbeyblade.org/Thread-4th-Season-MR-System