Hello,
2022 280 dq250 owner here,
Been running JB4 for 2 years and just went to a racingline flash
to answer your questions:
1. I haven't removed mine since installation and i haven't had any issues, at least for me, but they made me sign a notice that there were additional wiring/wires on my 2nd service, so i would advise removing it before servicing.
2. it reads the data from the obd2 so any safety features i assume would be hampered, i would leave it plugged in for best performance.
3. our gearboxes are different so it may differ but its enough even with the jb4, TCU tune would be safer when adding a downpipe and a remap.
4. the only disadvantage is always running highest quality fuel and that its not as smooth power delivery as a full-on flash, below 3.5k rpm it is perfectly normal it's only when you get on boost is where you'd feel it
5. no slippage for me but i had to cut boost by 50% when shifting because it would sometimes overboost if floored at high rpms and shifting at redline (auto) which would revert it to a safety map or map 0
although a remap is smoother, the performance is pretty close,
jb4 map 6 ran 4.49 0-60
racingline stage 1 + TCU ran 4.38
Good luck.