Making your website accessible is essential not only to comply with the law but also to have a successful online presence. Accessibility widgets promise your to make your website compliant to accessibility standards but do they? Legally speaking, websites need to be inherently accessible and a widget doesn't really meet that obligation. Widgets also have many drawbacks which make them unfit as a solution for making your website accessible.
Conflicts with screen readers
Most accessibility widgets try to recreate screen reader functionality (usually poorly) and ask users to disable their screen reader. A user with disabilities would then need to disable the screen reader they've become accustomed to in order to use an inferior version in order for the site to work properly.
Assistive technologies like JAWS, NVDA, and VoiceOver have specific settings and configuration that will be incompatible with widgets or superfluous. Worse, if the user's preferred screen reader is not disabled, all the content is read aloud by two different screen readers simultaneously.
Most features are redundant or fluff
Many accessibility widgets use the ability to change the size or color of text as a selling point. This functionality is in baked into browsers by default so it's totally worthless for an accessibility widget to offer. Any user that has trouble with small font sizes will have already increased their browser's minimum font size for all websites.
Other features offered like a reading line, a customizable cursor, or the ability adjust contrast, brightness, or saturation are already available in browsers or can be supplemented by browser extensions. Accessibility software that sells these type of features just want to make a quick buck off of those that don't know better.
Automated repair is unreliable and insufficient
Accessibility widgets will also offer the ability to scan your site (maybe even with AI, wowee!) and automatically fix issues that are making your website inaccessible. For trivial issues this might work; identifying missing alt text on images, missing form field labels, improperly displayed links, ect. But it also may make mistakes and incorrectly identify images or put the wrong label on the wrong element. It also won't detect sneakier problems like focus traps, illogical focus order sequences, and missing and incorrect captions for videos.
The wrong philosophy of accessibility
Widgets unfairly take the responsibility of making a website accessible away from the website owner and hoist it on the user. It would be akin to a brick and mortar business giving a disabled customer the tools and material to build a wheelchair ramp instead of building one themselves.
Many widgets will have an option that can be enabled to stop animations. This seems like a great feature for people prone to seizures but if they've set their system preferences to "prefers reduced motion" they shouldn't need to enable an option in order to make your website accessible. That's your responsibility as a website owner to ensure seizure-inducing animations don't show for people with that system setting enabled.
Accessibility is a commitment to a specific way of development not a widget or a script that can just be haphazardly added post hoc. Accessibility issues need to addressed at the source in order for there to be an acceptable fix.
What's the solution?
People. Computers and AI are good at a lot of things including detecting superficial accessibility errors, but using a website like a individual with a disability isn't one of those things. Comprehensive manual user testing is the only way to completely ensure your site is in compliance with WCAG guidelines.