---
title: "Reviews — 21x21x1 air filter - Flapen"
canonical_url: "https://flapen.com/research/us/tools-home-improvement/21x21x1-air-filter/reviews"
last_updated: "2026-08-08T07:59:54.515Z"
locale: en
meta:
  description: "Niche score 52/100 · $348K/yr market. Brand-locked demand (top 5 brands take 100% of clicks) keeps it on the watch list. Data updated Jul 2026."
  "og:description": "Niche score 52/100 · $348K/yr market. Brand-locked demand (top 5 brands take 100% of clicks) keeps it on the watch list. Data updated Jul 2026."
  "og:title": "Reviews — 21x21x1 air filter - Flapen"
---

# **21x21x1 air filter**

**Worth a look**

Shows sweet-spot pricing room ($26.30–$80.70), but brand-locked demand (top 5 brands take 100% of clicks) keeps it on the watch list.

Market size 53Growth 71Conversion 82Competition 20Returns 83Price range 95Avg price 92Brand share 0Review moat 43Quality gap 20

**Price range**

**Incredible****$26.30–$80.70**

cheapest to priciest tracked listing — scored on the share inside $15–$100

**Avg price**

**Great****$54.08**

avg listing price — sweet spot $15–$100

**Returns**

**Great****1.6%**

return rate — above 5% kills the launch gate

**Conversion**

**Great****8.8%**

search→purchase rate — share of searches ending in a sale

**Growth**

**Good****+53.4%**

90-day search growth — must beat 0% to launch

**Market size**

**Good****$348K**

$348K/yr · 73K searches

**Review moat**

**Okay****2,243.73**

avg incumbent reviews — the moat a new listing must climb

**Competition**

**Bad****77%**

top-5 click share — a locked-up shelf

**Quality gap**

**Bad****4.7★**

avg incumbent rating — lower means beatable quality

**Brand share**

**Bad****100%**

top-5 brand share — brand-locked demand

**Signals**[** High Price**](https://flapen.com/research/niches?market=us&signal=high_price "Avg price > $50")

## Reviews