Heh, those applications are always bullshit.
If you're using a regular home user connection, you're likely either on a bandwidth limited connection such as DSL, or on a hard traffic limiting connection like cable.
Bandwidth limiting in this case refers to actual bandwidth, not throughput. That is, the spectrum of available frequencies configured on the DSL modem, and allowed by the DSLAM, are set in stone. You can't transmit more traffic than your spectrum allows for. It's not physically possible. The frequency spectrum may be unlimited in local loop configuration, and your connection rate-limited by a distribution device farther upstream, but it's an unusual scenario.
Hard traffic limiting is usually a configuration on your CPE, which would be your cable modem for your cable connection. It's a configuration setting, and unless exploitable bugs are found in the software, it's impossible (and often illegal) to exceed this limit.
Even with straight metro ethernet connections, pretty much all providers set their policy maps to drop packets on exceed, and limit burst traffic strictly. That means that while you might have an initial burst of traffic for a second or two, any any packet in a steady stream of traffic that exceeds the limit will simply be dropped.
These "magic" bandwidth boosters typically rely on just multi-homing downloads like any other download manager.
