Optimizely vs Rebuy: Shopify Performance Comparison
Optimizely wins with Grade C vs Grade D — a one-grade performance difference that compounds on mobile devices.
Both apps provide personalization and product recommendations functionality for Shopify stores. This page presents StackConflict’s independent lab results for both — measured in a clean-room environment with no other apps installed.
Head-to-Head Metrics
| Metric | Optimizely | Rebuy | Faster |
|---|---|---|---|
| Overall Grade | C | D | Optimizely |
| JS Payload | 292.24 KB | 732.41 KB | Optimizely |
| CPU Desktop | 37 ms | 126 ms | Optimizely |
| CPU Mobile | 142 ms | 475 ms | Optimizely |
| Layout Shift | 0.0 | 0.0 | Optimizely |
Mobile CPU measured with 4× CDP throttle (mid-range Android). Tested 2026-05-30.
Optimizely — The Faster Option (Grade C)
Optimizely scores Grade C with a JS payload of 292.24 KB and 37 ms desktop CPU execution. Mobile CPU: 142 ms. Even as the faster of the two options, merchants on mobile-heavy stores should weigh its impact on their combined app stack.
View full Optimizely speed report →
Rebuy — The Heavier Option (Grade D)
Rebuy scores Grade D with a JS payload of 732.41 KB and 126 ms desktop CPU execution. Mobile CPU: 475 ms. This places it in the heavier half of StackConflict’s benchmark dataset — merchants running mobile-first stores should evaluate whether the feature value justifies the performance tradeoff.
View full Rebuy speed report →
When to Choose Optimizely
- Its unique feature set has no lighter equivalent in StackConflict’s database
- Your store traffic is predominantly desktop
- You have already removed or lightened other heavy scripts to compensate
When to Choose Rebuy
- Its unique feature set has no lighter equivalent in StackConflict’s database
- Your store traffic is predominantly desktop
- You have already removed or lightened other heavy scripts to compensate
Performance Verdict
Winner: Optimizely — Optimizely wins with Grade C vs Grade D — a one-grade performance difference that compounds on mobile devices.
Both apps carry Grade C — see StackConflict’s full Personalization rankings for lighter alternatives.
About This Test
StackConflict measures each Shopify app in an isolated clean-room environment — a single development store, no other scripts, Playwright-controlled browser. V8 CPU cost is the ScriptDuration delta before and after injection. CLS is captured from the same browser session. Results represent the median of three independent runs with outliers removed.
Data from the StackConflict Lab. Last updated 2026-05-30.