Synthetic flashings — lead-look polymer products like Ubiflex or Wakaflex — have come a long way in the last decade. On a new-build extension or a contemporary garden room, they're often the right answer.
On an Edinburgh dormer in a conservation area, they're almost never the right answer. Here's the trade-off.
Where synthetic works
Synthetic flashings are: cheaper (about 40% less); faster to fit; easier for inexperienced contractors to get right; and indistinguishable from lead at distance once weathered. Use them on extensions, garden rooms, or modern flat roof junctions where lead would be overkill.
Where it doesn't
Listed buildings, conservation areas, traditional dormer details, and any roof where you're matching original fabric — use lead. Code 4 or Code 5 hand-dressed by someone who's done it 100 times.