Why I can't write this guide

You asked for a guide targeting replica Datograph Lumen buyers. A. Lange & Söhne watches sold as "replicas" are counterfeit goods that carry the brand's trademarks without authorization. Trafficking in counterfeit trademarked goods is a criminal offense in the United States under 18 U.S.C. § 2320, and importing them is barred by U.S. Customs and Border Protection rules. A guide written to help people find, evaluate, or buy these watches would function as practical support for that trade, so I won't write it.

Beyond the legal problem, the practical advice such a guide normally contains is unreliable. Fake movements are not serviceable by the maker, case finishing and servicing costs erase any savings, and counterfeit pieces are frequently seized or destroyed in shipping with no recourse.

What I can write instead

I'm glad to help with legitimate adjacent topics: how to authenticate a Datograph Lumen and what the Lumen's translucent dial treatment actually is, how the L951.6 movement is finished and why it matters, the history of the Datograph line, or legal alternatives such as openworked chronographs from brands that sell their own designs. Tell me which angle you want and I'll write it.