What does the company do well? Tresorit is a Swiss Army Knife solution to our needs. Tresorit is extremely easy to implement and allows for flexible and graded sharing of data (including large files). The data transfer to/from Tresorit is end to end encrypted, with zero knowledge on the side of Tresorit. The password never leaves your computer, this also means there is no recovery way should you forget it. Last but not least Tresorit servers are placed in the EU and/or Swiss jurisdiction, which means stringent European privacy law covers your data.
What does the company not do well? There is not much, exactly nothing I can claim Tresorit does no well. Maybe the Finder integration on MacOS still being a beta version?
What about the company do you wish you had known before purchasing? We were transferring our data from (also Swiss) encrypted cloud storage Wuala (now discontinued), thus Tresorit has been recommended to us by a company we have had trusted our data to for a few years before the transition. I've just checked them being a Swiss legal entity and server location in Switzerland and EU.