Yes, your apprehension is understandable. We have spoken about it many times before, but nothing has come of it just yet. However, now it finally seems that the multi device feature for WhatsApp is in the final stages of testing and could very well be ready for a WhatsApp Beta version rollout in the coming weeks. The multi-device support will allow WhatsApp users to log in with the same WhatsApp account on as many as four different devices. It is also believed that WhatsApp is planning to roll out a new modern UI, at least for the desktop clients. While it is not clear as to when exactly the new WhatsApp beta will roll out, but it is to be expected that WhatsApp Beta for Android and WhatsApp Beta for the Apple iPhone will both get this new set of features for beta testers to experience, before a final rollout for all of us.
The good folks over at WABetaInfo suggest that while some components of the multi-device support are still not ready, chat history sync, muting chats and starring a message are ready. It is expected that by the time WhatsApp Beta users get access to this feature, all the components for it to work are ready. The multiple device support for WhatsApp accounts will mean that you will be able to log in with your primary WhatsApp number on up to four different devices, including the desktop and tablets. Whether you will be able to replicate this on another phone remains to be seen. The party piece has to be the ability to use WhatsApp on any of these devices irrespective of whether your primary phone is switched on or whether it has internet connectivity or not. The chat history migration as well as chats across devices will remain end-to-end encrypted, as WhatsApp has claimed with chats on the platform thus far.