Those exchanges use KYC only when using important amount.
Depending on the exchange you use, that might true, but there are various ways to track you even if you don't perform KYC verification such as cookies (e.g. google reCAPTCHA)
Coinjoin is putting different amounts of BTC from different persons in one or several transaction and then getting several outputs with the same amount so that It is difficult to know to whom the outputs are.
But if your name is tied to a transaction and another transaction in the coinjoin process is tied to criminal activities, The authority will make no distinction even if you are not involve.
That also apply with mixer
Mixer way of working are not so different from coinjoin. You put some BTC with other people's BTC, then several transaction are done. Then you recover your BTC on different addresses.
Mixer : you fully trust the mixer operator, from not logging mixer activity to not steal your coin
CoinJoin : you have control over your coin, since you only need to sign CoinJoin transaction you approve
are you from chipmixer (because you promote it)? is it reliable?
Yes, if you're looking for mixer service. But i prefer Wasabi CoinJoin over mixer service.