While I understand (and share) the caution around licenses, I don’t think this concern applies to Keep. With 99% of our codebase under the MIT license, it’s a far cry from just having "parts of the code with an open source license."
I recommend running Keep locally and comparing the Open Source version to the playground where full version is running. You might find it challenging to spot the differences.
I also reccomend comparing Keep Open Source to BigPanda and Moogsoft. It may be surprising how much of it Keep OSS, real MIT-licensed Keep has.