You can easily configure iStatistica to automatically stay in the menu bar. Just click settings and enable "Open iStatistica at Login" option. If you prefer using Notification Center widget only, you can safely disable autorun feature. iStatistica in Menu Bar and Notification Center widget can work independently. Temperature and fan speed monitoring requires installing a free plugin. AppStore apps are very limited in getting cpu, memory, disks temperatures and fan speeds, also disk read/write statistics can be done only in separate app. Thats why plugin is required.