Collections Add to Cart vs Monster Upsells: Shopify Performance Comparison
Both apps score Grade C — Monster Upsells has the edge with 17 ms vs 21 ms desktop CPU execution.
Both apps provide post-purchase upsell and cross-sell 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 | Collections Add to Cart | Monster Upsells | Faster |
|---|---|---|---|
| Overall Grade | C | C | Tie |
| JS Payload | 185.75 KB | 214.5 KB | Collections Add to Cart |
| CPU Desktop | 21 ms | 17 ms | Monster Upsells |
| CPU Mobile | 74 ms | 76 ms | Collections Add to Cart |
| Layout Shift | 0.0 | 0.0 | Collections Add to Cart |
Mobile CPU measured with 4× CDP throttle (mid-range Android). Tested 2026-05-30.
Monster Upsells — The Faster Option (Grade C)
Monster Upsells scores Grade C with a JS payload of 214.5 KB and 17 ms desktop CPU execution. Mobile CPU: 76 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 Monster Upsells speed report →
Collections Add to Cart — The Heavier Option (Grade C)
Collections Add to Cart scores Grade C with a JS payload of 185.75 KB and 21 ms desktop CPU execution. Mobile CPU: 74 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 Collections Add to Cart speed report →
When to Choose Collections Add to Cart
- 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 Monster Upsells
- 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
Result: Comparable — Both apps score Grade C — Monster Upsells has the edge with 17 ms vs 21 ms desktop CPU execution.
Both apps carry Grade C — see StackConflict’s full Upsell 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.