The title reads like a new encryption library for in the browser but in reality is an (advert for) encryption service, the SDK is open source because it requires your backend with its "Trustchain", the wording on the website is vague about how the Trustchain Private Key is "obtained".
Regarding the service, my main issue is that with an open source SDK you're aiming at a certain type of people, developers, like many of us, but I see no mention of the algos used which immediately causes me to lose interest (between that and the sales/marketing heavy website). If you're really targeting developers I would suggest losing the marketing babble and get down to brass tacks.
And finally, if the private key really is generated on your service, we can just pack up and go home.
What it sounds like you have is a PKI infrastructure with open source SDK and "end-to-end" encryption of things, as much as end-to-end applies for keys/trust roots generated anywhere but locally.
If any/all of this is wrong, please clarify.