Have used Febi before, top mount for wife’s BMW i3, VW brake shields, that sort of thing. A 3.0 TDI is a different kettle of fish though. I have an A4 Allroad with 3.0 TDI, so know it’s heavy. Pretty sure the front and rear (front suspension) lower arms are hydra bushes, so basically fluid filled. Lemforder as you say is OE. Only other thing I’d consider is Meyle HD as comes with 4 year warranty. I broke a rear spring on my car and fitted Lesjöfors after cross checking part numbers. Car is jittery as anything, so that’s all coming back out and I’m fitting genuine Audi. With suspension, don’t cut corners. Not saying Febi is bad, but those arms will last fraction of OE Lemforder arm, plus you’ll have labour again to swap out.