VERY useful. I searched for a plugin that had WAVE scanning integrated and this plugin came up. I was a bit hesitant because there were only a few reviews and the price was higher than most plugins. However, if the plugin worked, it would save me $1,000 from requesting a WAVE scan of my entire site. In short, this plugin is amazing. It is super-detailed. That makes it a bit longer to learn and master. However it makes it amazingly useful. If you take compliance seriously, this is the plugin for you. I am not a developer, but understand more about coding than the average content creator. I was able to understand this plugin, though it took several hours. Don't take that as a bad thing. It was necessary, and I learned a TON about ADA compliance in the meantime. When I had a question, the author was super-fast and helpful. I highly recommend this plugin.
I should mention one caveat to all of this. Businesses that are required to comply but don't have the ability to bring their websites into compliance can provide an accessible alternative to provide the same information, goods, and services that they provide online, like a staffed phone line. The trick, however, is that this option has to provide at least equal access, including in terms of hours of operation. And, as we know, the internet is around 24/7, so good luck with that.
The guidelines are broken down by four main principles: perceivable, operable, understandable, and robust. Under each principle, there are guidelines that provide specific goals a website should work toward. Under each guideline, there are testable success criteria. Those criteria are graded A, AA, or AAA. This grade shows the level of conformity to accessibility, AAA being the highest. The law only requires A and AA guidelines to be met.