There are speedo's that don't like that kind of wire up for the booster as well (While Tekins definitely need that setup to work). Hobbywing Justock are one of those who don't work well in that kind of wiring arrangement. If you wire in like that and don't disconnect the red wire from the ESC to the RX you'll burn up the booster.
I ended up just using the booster like you would on an airplane where I just passed through the signal wire and let the booster boost the BEC Voltage to the RX for my Justocks and it works just fine.
Many ways to get the job done, but be careful, and read what your ESC MFG says about wiring in a booster before you do it. If you do it wrong you could be out a booster, or toast the BEC in the ESC.