The thing is, I just notice that it says the frequency bandwidth is 100KHz, does that mean they are not going to work at mains voltage frequency (50Hz) or that they are a bit overkill and will work up to 100KHz?
They will work at 50 Hz. The 100 kHz bandwidth is more of a measure of transient response, that is, how well they will "track" a sharp turn-on or turn-off of current. Have a look at figures 9 and 10 in the datasheet. The "step response" is directly related to the bandwidth and are probably more useful but not as easily quantified by a single number.
Did you notice they are out of stock and not expected until 08/06/11?
: compatible with Arduino UNO, 24V operation, all I/O's fused and protected