As a relative newbie to the world of high horology, I've derived tremendous pleasure from admiring and owning the Lange 1815 Up/Down in pink gold. I wanted to share my experience and hope it will be helpful to others.
I first saw the Lange 1815 almost 6-7 years ago (interestingly back then the boutique was offering a discount!) The vintage Arabic numerals, blue hands, and the pervasive beauty of the watch immediately captivated me.
Recently, I finally purchased this exquisite timepiece, complete with a glossy blue Lange strap from the boutique that brings the watch to life and allows it to be worn more casually.
After wearing this watch quite frequently, a few observations that struck me.
The watch is surprisingly resilient for a precious metal piece, as it has picked up very few scratches or dings. In contrast, my PP Calatrava feels a lot more dainty and fragile, picking up fine scratches easily - I have to worry about it a lot more if worn casually. The watch wears nicely on the wrist with the right level of heft, feeling very balanced.
Viewing the watch on a projection screen fully zoomed in, I was amazed by the refined balance cock and hand carvings, which are absolutely flawless. The winding mechanism is not as smooth as a Lange 1, tending to resist or "roll back." I'm told this is normal for this watch.
I quite like the Lange straps, (which I believe are made by Camille Fournet). The bolstering complements the watch really well and is also quite resilient, handling minor spills.
Overall, I have to say there is a significant difference in the quality of this watch compared to its peers - I am constantly reminded of it when I rotate watches.

