Emarsys vs Flashy: Shopify Performance Comparison
Both apps score Grade B — Emarsys has the edge with 5 ms vs 21 ms desktop CPU execution.
Both apps provide email marketing and automation 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 | Emarsys | Flashy | Faster |
|---|---|---|---|
| Overall Grade | B | B | Tie |
| JS Payload | 58.46 KB | 42.34 KB | Flashy |
| CPU Desktop | 5 ms | 21 ms | Emarsys |
| CPU Mobile | 60 ms | 83 ms | Emarsys |
| Layout Shift | 0.0 | 0.0006 | Emarsys |
Mobile CPU measured with 4× CDP throttle (mid-range Android). Tested 2026-05-30.
Emarsys — The Faster Option (Grade B)
Emarsys scores Grade B with a JS payload of 58.46 KB and 5 ms desktop CPU execution. Mobile CPU: 60 ms. It passes every StackConflict threshold for payload, CPU, and layout stability — making it safe to install on any storefront including mobile-first stores where Time-to-Interactive directly impacts conversion.
View full Emarsys speed report →
Flashy — The Heavier Option (Grade B)
Flashy scores Grade B with a JS payload of 42.34 KB and 21 ms desktop CPU execution. Mobile CPU: 83 ms. Performance is acceptable but worth monitoring, particularly on stores with high mobile traffic share.
View full Flashy speed report →
When to Choose Emarsys
- You need its specific features and can monitor its mobile impact
- Your other apps are lightweight (Grade A) so there is headroom
- You are on desktop-skewed traffic where CPU cost matters less
When to Choose Flashy
- You need its specific features and can monitor its mobile impact
- Your other apps are lightweight (Grade A) so there is headroom
- You are on desktop-skewed traffic where CPU cost matters less
Performance Verdict
Result: Comparable — Both apps score Grade B — Emarsys has the edge with 5 ms vs 21 ms desktop CPU execution.
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.