I have run a lightened and balanced flywheel in my TDI for 4 years. Absolutely love it. Car would not perform the way it does with a heavy flywheel.
I have put on 140,000 k's with the lighter flywheel so they are just as durable.
No problem with shifting,been doing that for 35 years so I think thats no issue for me.
I quess it depends who does your lightening ,how they do it and how much attention they pay to balancing it. Anyone can lighten a flywheel,but if you don't know exactly what you are doing with a TDI flywheel you will get what you pay for..