Client-side vs server-side: the flicker tax

Client-side vs server-side: the flicker tax
Shipped a hero test Friday on client-side (Optimizely snippet). Tuesday: support tickets about the page 'jumping.'
That's flicker. FOOC. Original loads, snippet swaps it, user sees the flash. Killed my variant before it had a chance.
Moved the same test server-side. Zero flicker. Variant suddenly +4%. Same idea, the client-side tax was hiding the win.
Tradeoff: server-side needs a dev to wire the flag. Client-side I can launch alone at 11pm. So:
— Copy/CTA/color test that's above the fold → server-side or eat the flicker.
— Below-fold tweak nobody sees load → client-side is fine, ship it solo.
Go open your variant on a throttled connection. Watch for the flash. Report back.