Monster Upsells vs Ultimate Sales Boost: Shopify Performance Comparison
Monster Upsells wins with Grade C vs Grade D — a one-grade performance difference that compounds on mobile devices.
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 | Monster Upsells | Ultimate Sales Boost | Faster |
|---|---|---|---|
| Overall Grade | C | D | Monster Upsells |
| JS Payload | 214.5 KB | 645.46 KB | Monster Upsells |
| CPU Desktop | 17 ms | 55 ms | Monster Upsells |
| CPU Mobile | 76 ms | 318 ms | Monster Upsells |
| Layout Shift | 0.0 | 0.0006 | Monster Upsells |
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 →
Ultimate Sales Boost — The Heavier Option (Grade D)
Ultimate Sales Boost scores Grade D with a JS payload of 645.46 KB and 55 ms desktop CPU execution. Mobile CPU: 318 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 Ultimate Sales Boost speed report →
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
When to Choose Ultimate Sales Boost
- 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: Monster Upsells — Monster Upsells 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 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.