[mwebb]

generic
will not give up much real time info in a VW Jetta -

it will not see most of the available DTCs and it will not run basic settings

the fuel trim values are going to read Measuring Block 032 adaptives
you need to see real time STFT and LTFT values

for the Jetta
you will need VCDS also called Vag Com from Ross-Tech

or
Auto Enginuity pro line or
Enhanced for the VW and the other car you have

AE and VCDS both will run basic settings and both will have enhanced data
VCDS is better for VW
AE is better for everything else and works for the VW
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edit;http://www.cobbtuning.com/products/?id=5027
never mind
it is not generic for the mazda but if it works at all on the jetta ,
it will be only generic

http://www.ross-tech.com/
for VW
this is better

http://www.autoenginuity.com/index.html
for every thing else , this is better and , AE works with VW

pricing is similar for all three IF only Mazda and VW are selected for AE