For me Java is a no no because of all the update and security problems with it. Beside it isn't a lightweight and fast platform. I know many people that waisted a lot of time with Java software upgrading problems because of broken backward compatibility.
The other problem is the pricing model. If I host everything and use my own bandwidth, what do I pay for ? Software development and upgrade ? This is very expensive for a user with a non profit activity who just want to stay in control with its own data.
As far as I understand there's no need to pay if you don't use the teams feature or don't have external collaborators.
Java seems to be a nice way to provide consistent experience across different platforms, I don't even want to think of installing OwnCloud on Windows. And with OwnCloud I'm even more concerned about security as it's written on PHP, but I may be biased here.
Even with Java this is miles more secure than something like Dropbox or other Cloud Storage where you host all your data on someones elses server. So yeah, Java as a technology choice might not be perfect but which other tech is flawless anyway ? Id argue that properly securing your servers/clients is a much bigger problem than someone exploiting the AeroFS software.
Pricing is for Teams only which makes sense, for everyone (teams of up to 3) its free, which is awesome!
The other problem is the pricing model. If I host everything and use my own bandwidth, what do I pay for ? Software development and upgrade ? This is very expensive for a user with a non profit activity who just want to stay in control with its own data.