Is the modified version of WhatsApp safe?

Yes, it is very safe and you will get more features than official WhatsApp; I would advise you to download its modified version in Android because it is an Android WhatsApp.

Is the auto-reply feature available in this Whatsapp Mod app?

Yes, you will also get the auto-reply feature in this WhatsApp. Apart from auto-reply, you will get many features in it. It is an app that comes with a modern and modern interface.