Nectifirm ADVANCED is a cream made for the neck and décolletage, where the skin is thinner, has fewer oil glands and moves constantly.
Here is the honest answer on what to expect. A good neck cream improves hydration, texture and the crepey look that comes from dryness, and that is a real and visible difference. What it does not do is tighten loose skin or lift a jawline. That is a structural change and no cream reaches it.
If you would rather not buy a separate product, taking your face serum and moisturiser down onto your neck is genuinely better than doing nothing. The one thing worth being strict about is sun protection, since the neck and chest show sun damage earlier than the face and are much harder to correct afterwards.