Back in Stock Alerts vs Emarsys: Shopify Performance Comparison
Emarsys wins with Grade B vs Grade C — a one-grade performance difference that compounds on mobile devices.
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 | Back in Stock Alerts | Emarsys | Faster |
|---|---|---|---|
| Overall Grade | C | B | Emarsys |
| JS Payload | 203.34 KB | 58.46 KB | Emarsys |
| CPU Desktop | 4 ms | 5 ms | Back in Stock Alerts |
| CPU Mobile | 27 ms | 60 ms | Back in Stock Alerts |
| Layout Shift | 0.0 | 0.0 | Back in Stock Alerts |
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 →
Back in Stock Alerts — The Heavier Option (Grade C)
Back in Stock Alerts scores Grade C with a JS payload of 203.34 KB and 4 ms desktop CPU execution. Mobile CPU: 27 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 Back in Stock Alerts speed report →
When to Choose Back in Stock Alerts
- 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 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
Performance Verdict
Winner: Emarsys — Emarsys wins with Grade B vs Grade C — a one-grade performance difference that compounds on mobile devices.
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.