Boomtrain vs Kiwi Sizing: Shopify Performance Comparison
Boomtrain wins with Grade B vs Grade D — a significant 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 | Boomtrain | Kiwi Sizing | Faster |
|---|---|---|---|
| Overall Grade | B | D | Boomtrain |
| JS Payload | 96.54 KB | 521.05 KB | Boomtrain |
| CPU Desktop | 21 ms | 70 ms | Boomtrain |
| CPU Mobile | 64 ms | 331 ms | Boomtrain |
| Layout Shift | 0.0 | 0.0 | Boomtrain |
Mobile CPU measured with 4× CDP throttle (mid-range Android). Tested 2026-05-31.
Boomtrain — The Faster Option (Grade B)
Boomtrain scores Grade B with a JS payload of 96.54 KB and 21 ms desktop CPU execution. Mobile CPU: 64 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 Boomtrain speed report →
Kiwi Sizing — The Heavier Option (Grade D)
Kiwi Sizing scores Grade D with a JS payload of 521.05 KB and 70 ms desktop CPU execution. Mobile CPU: 331 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 Kiwi Sizing speed report →
When to Choose Boomtrain
- 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 Kiwi Sizing
- 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: Boomtrain — Boomtrain wins with Grade B vs Grade D — a significant 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 2026-05-31.