Why I need to buy KESS V2 and Ktag programmer together?

From sally:

KESS V2 is a ECU programming tool that is perfect for OBD use, while KTag is perfect for Jtag, BDM and all the Boot application (tricore and ST10).

With KESS V2 you programming directly through the OBD port of the vehicle, while with Ktag (Ktag 2.13) you need to take apart the ECU and open it, after you can make the read/write operation.

Many ECU has the advantage that can be read and write from OBD port (so KESS V2 is perfect), but there are lot ECU that need to disassemble from the car and open and this is the case for all the ECU that need to be programmed with Jtag, BDM and Boot protocols, so KTAG is needed.

2.13V Ktag Master V6.070 Plus V2.15 Kess V2 Unlimited Token V4.036 with Free ECM TITANIUM V1.61 Software:

kess v2 plus ktag