I am on BE for half a year now, and my playing gets worse.

Also 29.. No, this is not good, indeed. In order to give some advice it is important to know exactly what you do - how long you do it - what mix of other exercises than BE you do? Just like any other method, BE can be overdone. Probably one or more of the things mentioned in 29. are not correct in your practice, but if everything seems to be OK, it is very well possible that you simply overdo it.. Also, doing BE and nothing else can be counterproductive in the end.You need to play on 'normal chops' to incorporate the newly learned things in your normal playing. It is also possible that you suffer from a short period of instabilty (mostly from a couple of days to a week).. Of course things are changing in the way you use your muscles and the way you play. Maybe you are in a phase of transition. For me, most of the time these periods are a prelude to a breakthrough.

It is possible that you still look upon BE as an embouchure. This can lead to too direct a change, which can lead to a lot of problems. It is very important to practice on 'normal (=changing/developing) chops and not work towards a certain lip setting. BE IS NOT AN EMBOUCHURE AND WORKS INDIRECT!!!

If this instability continues, you might need to take a few steps back in your lesson plan. You can also cut back on the time you spent on BE or try experimenting with doing BE every other day or three times a week. Just skipping a week of BE can be wholesome. Muscles need time to adjust to the new way of using them.