This got picked up privately by @maria but she said I could repost in case it is of interest to others:
"SiteImprove is a good service for monitoring and reporting on various aspects of the accessibility of a website. I don’t have extensive experience of it, but I was impressed with how in depth it is able to go - even reporting on the readability of different pages etc. We are interested in building our own, open source version of it, but that’s probably some way off!
However, if I understand correctly, Browsealoud is an add-on to the website itself, giving users of the website different ways to interact with the site.
There is some debate about whether or not these services help or hinder the accessibility experience, however I think the problems are when the underlying site isn’t fit for purpose. Sometimes such plugins are added on to sites that aren’t very accessible in the first place, hoping to magically fix any existing problems. There is an argument that when a site is well built, these services make accessibility more visible - perhaps to people who don’t need assistive technology, but do find websites hard to interact with.
Depending on the needs of your particular users, it might be that you could build the functionality or fixes you need natively into the site for a comparable cost of using their service.
Anyway, I realise I have said a lot but haven’t actually answered the original question - I’m afraid I don’t know of better alternatives, but I believe that Browsealoud is a respectable product. I’ll certainly keep my eyes open, and your question has piqued my interest, so I may delve into it a bit."