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!