The ERGObrass helps you to keep a good posture and breathe more freely and efficiently. Would it not be better to lean, or even hang, your arms on the horn rather than keep them continually tensed up?

You need some time to readjust your perception about trumpet playing. You need a moment to get used to the different feeling of the nearly weightless instrument. You also need to practise how to handle the instrument when not playing, empty the water etc. Everything cannot obviously be done exactly the same way as before, but the new way is not any worse, just slightly different. After the learning period, you will enjoy playing with less tension.

Only after you have learned to play with it you can say whether it is good or not. But like always, it is a lot easier to condemn something new without even trying it out!