The OM606 already has the vacuum control system built in. This is both good and bad.
Good: because I think it will correctly and automatically operate the variable vanes.
Bad: because using vacuum to position a wastgate doesn't work properly at high altitude.

Background: To pull the wastegate fully closed, the ECU directs full vacuum to the vacuum cylinder. At sea level the vacuum cylinder has about 15 PSI across it. This successfully pulls the wastegate closed. At 10K feet there is only 10 PSI across the vacuum cylinder and the wastegate isn't pulled all the way closed. This is quite simply a design goof, they must not have designed for nor tested at altitude.

That is why I'd rather go for the electronically controlled VNT. I can easily convert the ECU signal into what the turbo wants. Even better I can make my own rules for VNT behavior. Getting information on fitment seems a lot harder.