Limit on USB cable length is dictated by overall USB architecture of having 5 hubs, and artificially-imposed time-out of device responses (due to half-duplex nature of USB 2.0 communication protocol). The worst-case connectivity model in USB 2.0 is:
Overall, per specifications, a USB host will wait 18 UI (18 * 83.33ns) = 1500 ns (in FS mode) before detecting a failure to respond, and will re-try the failing packet in hope of self-recovery.
The 1500 ns is the time of signal flight in both directions. Assuming the device worst case response of 400 ns, this leaves 1100 ns for signal flight, or 550 ns in one direction. Again, assuming typical dielectric qualities of USB cables, or 5.2 ns/m, this gives a working distance of 105 m, or up to 300 ft. So, theoretically speaking, a single FS device should be working over a 300-ft bare cable.
In practice the USB over CAT5/6 extenders use some up-conversion into truly differential Ethernet-like signaling, and use some silicon ICs to do so, which incurs digital propagation delays. As result, practically-achievable distance comes down to about 150 ft:
Please note the words "single USB device" in the product description. So be cautious: if you use this extender behind even a single external USB hub, the link will likely fail.
Also be aware that USB host designs are listening to the bus and checking if the bus is in idle state before making a decision to transmit next packet. A 50-100 ft bare cable in FS mode will produce massive reflections beyond the transmitted End-Of-Packet (FS bus is not terminated with 45-Ohms unlike in HS mode). Some overly-constrained USB host designs might construe these reflections as unsolicited bus activity, and the host port might shut itself down.