I have been using the DEVONthink 3 alphas and betas since the inception of the DEVONthink 3 program. I started using DEVONthink 3 exclusively (deprecating DEVONthink Pro Office 2) about 6 months ago. As someone who uses the app 8 - 12 hours / day, I can say DEVONthink 3 has been very stable throughout this process.
I stopped using DEVONthink 2 in favor of DEVONthink 3 because D3 is significantly better for anyone who manages large quantities of documents across numerous active, complex projects.
I have always advised people “do not buy DEVONthink if you do not know why you need it”. And, do not expect glam – expect a deep set of tools that will take some time to align with your needs.