I use Bluetooth with AVR embedded system at 115.2 kbaud non prefix mode without problems.
Here are things that worked well for me.
The newdata event concatenates packets, checks for start and end, then processes. Then it deletes processed packet from buffer. The integrity of handling newdata received bytes is very important.
The tablet commands are mostly small packets for soft buttons and timer requests for information from the embedded side. The embedded packet back to the tablet, contains information about the packet, so the tablet can process properly. The tablet updates numeric values, plots data, data logs .... I have not experience problems with data logs happening, along with real time plots, numeric updates, navigation of modes and tables on embedded side via tablet soft button controls.
From a user interface 50 mS response is often good enough. I have found timers set to less than 100 mS have jitter, but that is likely an Android issue.
The B4A application was similar to an already debugged and tested VB6 rs232 application in conjunction with embedded system.
I use a Saleae Logic analyzer to capture both rx, tx at the TTL embedded side, to insure confidence there.