No, not an engineer. Just a car enthusiast. I have no personal experience with BG 109 but as I've written before, I'm quite active over at BobIsTheOilGuy and there are a wide variety of people posting with car problems and I've not seen many great success stories for these cure-all oil additives. BTW you do realize that with regular oil changes of a name brand oil you'll get a clean valve cover and valvetrain? There's no need for additives in a modern API motor oil. Those are *maybe* necessary in a severely neglected motor or a known sludger (1.8T guys, I'm looking at you).
BG44k is a good product but it's a professional-grade one. It uses the same active ingredient as products like Red Line SI-1, Techron Concentrate, and Regane: PEA.
My question for OP, and anyone else thinking they need all these special additives: why do you think your motor oil needs to be supplemented? What is the oil not doing? How do you know problem XYZ is caused by the oil? I get the feeling people see an advertisement or notice some in-store display and suddenly think their oil is lacking...protip: it isn't. If you read up on the strict requirement imposed by ACEA A3/B4 and VW 502/505, you'll likely reach the [correct] conclusion that you don't need or want those products.
If the OP said "well I pulled my valve covers and there was way too much varnish and sludge, and my oil pan has a coating of sludge", then yes, I'd be inclined to recommend a different approach, such as several back-to-back short-interval changes.