If you're using a wood reducer (or any reducer) it has to be anchored solidly. If not it will "rock" with foot traffic and degrade quickly.

Wood reducer:
With a new floating floor system the ideal situation is to anchor on the old side only. Then the new system can still float.
A good fastener for this is called a trim screw. They give you screw-like holding power with a nail-like penetration holes.
Drill pilot holes and use a quality adhesive on the fastener side only.

There is also a stainless steel trim screw available that is outstanding for doing trick, exterior deck and fascia work.
The new Battleground Community Center required 2x12 CVG fir fascia and these screws along with Gorilla waterproof glue made it happen.