Client-side A/B tools add a median 380ms flicker delay; server-side adds ~0ms but costs ~4x engineering hours

Client-side A/B tools add a median 380ms flicker delay; server-side adds ~0ms but costs ~4x engineering hours per test.
Latency measured on 50 real test deployments, p50.
Client-side (snippet in head) flickers the original before the variant paints — measurable conversion drag on slow connections. Server-side renders the variant clean but needs a deploy per test.
— Client ▮▮▮▮▮▮ speed-to-launch, ▮▮ render quality
— Server ▮▮ speed-to-launch, ▮▮▮▮▮▮ render quality
Use server-side for above-the-fold and checkout; client-side for fast copy tests.
Read the number, not the story. [n=50 deploys · p50]