Hiya,
There's a matrix of ebook properties
here which includes text to speech. You may have to check out the relevant device forums for users with more day to day experience of this particular function.
Having a quick scan - it looks like the Hanlin and Hanvon models all have it but its not a common feature to other eink devices.
In this instance to be honest I'd just buy the titles you want in whatever format they are and then see apprentice alf - oh and don't forget to use Calibre for your library - cant go wrong then.
Edit: Probably worth noting that sighted users of text to speech may miss out some issues a visually impaired person would have as I'm sure your aware
