# Secret KB vs Underlayer

The clearest difference is price: Underlayer at Free against Secret KB's $0.99. Secret KB's advantage is in-app purchases (none vs 1) and ads (none vs shown). On device support and iOS requirement there is nothing between them.

Underlayer is free to download; Secret KB costs $0.99 up front. Underlayer sells 1 in-app purchase, starting at $2.99 per 7 days. Secret KB asks for nothing beyond the download.

Secret KB ships an update every 10 days, Underlayer every 5 months. The most recent releases landed on September 14, 2026 and September 12, 2026 respectively.

## The numbers

| Metric | Secret KB | Underlayer |
| --- | --- | --- |
| Price | $0.99 | **Free** |
| In-app purchases | **No** | Yes |
| Ads | **No** | Yes |
| Update frequency | **Every 10 days** | Every 5 months |
| Size | 6 MB | 169 MB |
| Requires iOS | **14.0** | 15.1 |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [Asadullah Jamadar](https://appshunter.io/developer/1655125846) | [Mihail Rukavishnikov](https://appshunter.io/developer/1648782212) |

## What reviewers say

### Secret KB

[App page](https://appshunter.io/ios/app/secret-kb/id1605391634)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### Underlayer

[App page](https://appshunter.io/ios/app/underlayer/id6753363956)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Premium | $2.99 | per 7 days |


## Frequently asked questions

### Is Secret KB free?

Secret KB costs $0.99, with no in-app purchases.

### Is Underlayer free?

Underlayer is free to download, with in-app purchases available.

### Do Secret KB or Underlayer have ads?

Underlayer shows ads; Secret KB does not.

### Which is updated more often, Secret KB or Underlayer?

Secret KB ships an update every 10 days, and Underlayer every 5 months. Most recently, Secret KB was updated on September 14, 2026 and Underlayer on September 12, 2026.

---

*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*