I always am a bit skeptical of these demos, and indeed I think they didn't put much effort into getting the most out of ElevenLabs. In the demo, they used the Brian voice. For the first example, I can get this in ElevenLabs [1]. Stability was set to 20 here and all the other settings were at their default. Having stability at the default of 50 sounds more like what is in the demo on the site [2].
Having said that, I'm fully in favor of open source and am a big proponent of open source models like this. ElevenLabs in particular has the highest quality (I tested a lot of models for a tool I'm building [3]), but the pricing is also 400 times more expensive than the rest. You easily pay multiple dollars per minute of text-to-speech generation. For people interested, the best audio quality I could get so far is [4]. Someone told me he wouldn't be able to tell that the voice was not real.
[1]: https://elevenlabs.io/app/share/3NyQKlL6EeOHpIDtL5pA
[2]: https://elevenlabs.io/app/share/TUx4yluXtV3pFTHr7Cl7