How capable are USB hubs? Their capabilities vary with manufacturers. A good (and USB Certified) USB hub would be self-powered (getting power from a wall adapter, not from the host port), will have individual port power protection/control. And will have an official USB-IF Certification logo. These hubs still sell for $40-$50.
A cheap (bus powered) USB hub would take the power to supply all connected peripherals from upstream (usually non-detachable) cable. Technically speaking, these "minimized" hubs (most of them) a cheats, because they report in their descriptors that they are "self-powered", thus lying the system. A bus-powered hub can/should supply no more than 100mA per port, and the system will deny any USB device that describes its power consumption above this limit (you will have a pop-up error message). So to be useful and avoid system power policy, these el-cheapo hubs must lie to the system. In addition, the port where this hub is connected to must have a lot of current sourcing capability to drive all four suggested devices (if they are NOT self-powered from wall-type adapters).
Bus-powered hubs have one big disadvantage with regard to quality of power delivery - power to any new attached device will go through the same piggy-tail upstream cable. As result, the initial voltage "droop" (on connect) will affect all other already connected devices, so they might disconnect. But if you are not planning to use hot-plug devices while the rest is operating, this might be of lesser concern.
In short, the Targus hub will give you full USB2.0 functionality on all four devices if all hard drives are "self-powered" with wall adapters. If not, you might experience functional instabilities. Or might not, all will depend on quality of your host port.