As much as i know, there is no helm chart for ECK operator however for the Elasticsearch stack there is a helm chart available.

Elastic stack helm chart : https://github.com/elastic/helm-charts/tree/master/elasticsearch

ECK is operate you can extend Kubernetes orchestration by YAML files or else you can create own helm chart as per need if required.

ECK quick deploy : https://www.elastic.co/guide/en/cloud-on-k8s/current/k8s-quickstart.html

ECK is providing official support in GKE however i think you have idea about the advantages & disadvantages of using ECK.