Chewing very much gives you an effect - especially with fresh kava, as dry root pieces are a little hard. Chewing powder would be messy and would end up just being toss n wash without the wash. But if you have some fresh green kava, chewing is an option
In southern Vanuatu - Tanna, Aniwa, Erromango, and also Tongoa in the Shepherds - the preferred prep method in villages (not commercial nakamals) is chewing to pulp, spitting out the mulch, adding water then straining. The chewer has to very careful not to swallow, and keeps stuffing more root in to absorb excess saliva so it doesn't go down the throat. Even without swallowing some kava is absorbed through the mouth, but the main effect when chewing is from small amounts of kava-infused saliva being swallowed. This undiluted juice is very strong. I once made a few shells on Tanna by chewing and some got down my throat and I was completely incapacitated.