How much you like Merlin really depends on your background. For users who are not good with writing code, it provides a nice GUI for accessing OpenAI models and as long as your workload isn't extreme or image heavy you will probably come out ahead by buying Merlin over subscribing to ChatGPT Plus. For comparison, my Merlin API key use is still under a penny but my use primarily involves asking Merlin to write code that I then execute against a separate API key for accounting purposes. My workload is almost entirely in GPT-4o because I am doing things like summarizing a section of a textbook where the input is too large for GPT-3.5-turbo and after writing about 1000 course descriptions my cost is around $17. I can do similar things to what Merlin does just using the ChatGPT developer console.

While the Merlin browser extension is a decent idea, I find it unusable in practice. The websites I tend to visit get super glitchy when code is injected into them. This is not unique to Merlin as password managers, spelling extensions, and anything else that injects code have similar effects ranging from the annoying scroll flicker to the frustrating where the keyboard randomly moves and you end up with garbled text. Your mileage may vary. What I have done is set Chrome where I need to click on the Merlin extension to activate it on a given page and as long as the site you are on can be safely reloaded, you are free to use Merlin on the same site for the lifespan of the browser tab. Merlin replaces a formerly free tool I used to skip over unnecessary commentary in websites. I like that I can try other models such as Gemini and Sonnet, but the Merlin magic feature seems overly biased towards using GPT-4o as the Sonnet model is supposedly better at coding tasks (it has been slightly better about producing functional code in my experience). Without transparency into how the web access mode works, I am going to say that it is only useful in certain contexts. For an academic researcher or an investor I can see the web access mode being useful. In my particular use cases, I am not wanting answers that are likely to differ much in the 6 months since the last update of the underlying models.

My takeaway: Merlin is a useful tool for people who must interact with massive amounts of content in their daily lives for which the convenience of not having to copy links is a massive time saver. If you are just getting started with AI you will have a library of prompts to help inspire you.