Frequently Bought Upsell vs Product Add-ons & Custom Options: Shopify Performance Comparison
Frequently Bought Upsell wins with Grade A vs Grade C — a significant 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 | Frequently Bought Upsell | Product Add-ons & Custom Options | Faster |
|---|---|---|---|
| Overall Grade | A | C | Frequently Bought Upsell |
| JS Payload | 11.1 KB | 157.55 KB | Frequently Bought Upsell |
| CPU Desktop | 4 ms | 25 ms | Frequently Bought Upsell |
| CPU Mobile | 17 ms | 152 ms | Frequently Bought Upsell |
| Layout Shift | 0.0 | 0.0 | Frequently Bought Upsell |
Mobile CPU measured with 4× CDP throttle (mid-range Android). Tested 2026-05-30.
Frequently Bought Upsell — The Faster Option (Grade A)
Frequently Bought Upsell scores Grade A with a JS payload of 11.1 KB and 4 ms desktop CPU execution. Mobile CPU: 17 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 Frequently Bought Upsell speed report →
Product Add-ons & Custom Options — The Heavier Option (Grade C)
Product Add-ons & Custom Options scores Grade C with a JS payload of 157.55 KB and 25 ms desktop CPU execution. Mobile CPU: 152 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 Product Add-ons & Custom Options speed report →
When to Choose Frequently Bought Upsell
- You are running a mobile-heavy store and Core Web Vitals matter
- You want to stack multiple apps without worrying about combined JS cost
- Conversion rate optimisation is a key priority
When to Choose Product Add-ons & Custom Options
- 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: Frequently Bought Upsell — Frequently Bought Upsell wins with Grade A vs Grade C — a significant performance difference that compounds on mobile devices.
Install Frequently Bought Upsell →
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.