A few months ago, I was looking for a tool that can be used to change VAG group clusters to g6/touran/Tiguan, etc., immo adaptation, making keys, and millage correction. 
Then I filter out two: Xhorse VVDI2 and Flyobd FVDI2
Reference:
VAG diagnostic:

VAG key programming:

Special functions for VAG:



From the diagram above, FVDI2 FLY and VVDI2 almost share the same functions.
Their differences are mainly in the following aspects:
1 OBD read CS/PIN of MED17
2 Generate OEM remote control
3 Software Authorization
 
FVDI2 full kit includes software for VAG – VW, Audi, Seat, Skoda; Porsche; Mercedes/Smart/Maybach; OPEL/VAUXHALL; BMW; Peugeot/Citroen; Fiat/Alfa/Lancia; Renault; Toyota/Lexus; Hyundai/KIA; Nissan/Infiniti; TAG Key Tool; Ford; Volvo; Chrysler, Dodge, and Jeep; Mitsubishi; DAF; Bikes, Snowmobiles, and Water scooters.
Your FVDI2 commander can be authorized; the cost depends on the vehicles
 
VVDI2 full kit includes VK-01 Transponder Programmer, VJ-01 Passthru J2534, and software for VAG – VW, Audi, Seat, Skoda; BMW; PSA (Peugeot/Citroen); Porsche
VVDI2 authorization service, see here:
https://www.xhorsemall.com/products/vvdi2-full-version.html 
Summarize:
I read a lot of information online before finally deciding which tool to buy.
I was told that if tools are only for VAG + BMW, then VVDI2 and VVDI prog is the best way to go. No need for any other tool. 90% of VAG and BMW can be done by OBD in VVDI2:
https://www.xhorsemall.com/products/vvdi2-full-version.html

VVDI programmers don’t have OBD, it’s for bench programming only. 
Compatible with CAS4, FRM, EZS, EWS4, etc.