Quick answer
A replica Zeitwerk 104.021 is a copy of A. Lange & Söhne's Zeitwerk, the German brand's jumping-numeral watch that launched in 2009. The 104.021 part is a seller catalog code, not an official Lange reference. Genuine Zeitwerk references sit in the 140.xxx series. So when that number shows up in a listing, you're looking at a dealer's internal SKU, not a model designation from Glashütte. What you get for your money depends on which tier of replica you're buying, and the honest answer is that none of them reproduce what makes the Zeitwerk interesting.
What the real watch does
The Zeitwerk shows hours and minutes as large numerals in a wide aperture instead of hands. At the top of every minute, both discs jump to the next value at the same instant. That snap is the complication. Lange builds it with a constant-force escapement and a patented jumping mechanism, so the minute doesn't creep, it flips. Below the aperture sits a small seconds dial. The case is white gold, yellow gold, or platinum, roughly 42mm across, and the movement is hand-wound, finished with Glashütte ribbing, blued screws, and an engraved balance cock you can study under a loupe for an afternoon.
Where replicas land
Photo-wise, the better replicas get close. Case width, lug shape, the oversized numeral font, the aperture framing, sapphire front and back. On a screen, at listing-photo distance, that reads as convincing.
In person the gaps show up fast:
- The jump. Most replicas run a quartz module or a modified automatic with slowly rolling discs. The minute drifts. If the listing doesn't state that the jump is instant and mechanical, it isn't.
- Weight and metal. Genuine examples are precious metal. Replicas are steel or plated brass, and the heft is different.
- Movement finish. Look through the caseback. Real Glashütte ribbing is crisp and even. Replica finishing usually looks stamped and shallow.
- Dial printing. Numeral edges, the signature, and the "Made in Germany" line are where cheap dials give themselves away.
What to check before ordering
Ask for photos of the actual unit, not renders. Get case diameter and thickness, because replicas often run thicker than the original. Find out what movement is inside and whether the discs jump or roll. Check the stated water resistance and whether the crown screws down. Read the return window. And if the reference number in the title doesn't match a real Lange model, ask which model it's meant to copy. A seller who can't answer that isn't tracking details.
Legal reality in the US
Counterfeit watches are trademark-infringing goods. US Customs and Border Protection seizes them at the border, and buying one for personal use does not create an exemption. Resale is infringement as well, so there's no exit. Practically, a replica also has no service path: the brand won't touch it, and plenty of independent watchmakers won't either, because parts don't exist.
Bottom line
If you want the Zeitwerk look on a budget, go in knowing you're buying the silhouette and nothing else. The jump, the finishing, and the metal are the watch. Price a replica as costume jewelry rather than an investment, and you'll be comfortable with it.