We are using Zoho Books and really impressed with the feature along with flexibility and control it brings to a small firm like ours. However, after trying out Zoho GST, I was really disappointed in the half-baked approach to this new product 

• Zoho Books doesn't have a way to restrict selected user only to "GST Filing", the user should have admin privilege to get access to "GST Filing", this led us to use Zoho GST in spite of duplicate feature.
• Zoho GST seemed to be promising, however, there is no "direct" integration even with the export/import option, it is not really compatible.  
• Lots of the mandatory "Column" in the Zoho GST is not available in the xls/csv exported by Zoho Books for both Sales/Purchase module
• Even the matching columns like Invoice dates, state are not in the format supported by Zoho GST