well.....been having a play today with my archos gmini 202 and the wifes creative muvo with my senny sp 25s
like i said,i'm no audiophile and certainly no reviewer but i'll try and offer some enlightment......
for specs etc, heres the link again:
http://www.bkelec.com/HiFi/Amps/headphone.htm
the amp itself is well built,with a nice front brushed alloy finish and a nice chunky, study knurled volume control knob,which also acts as a push switch.
well the link says it all really....would have been nice to have a choice of finishes,black for instance but a minor gripe really.
one thing they dont mention is that the amp comes with a 9V battery and 2 seemingly decent quality screened audio leads,1 50cm and 1 94cm so assuming you've got a player and headphones

you're ready to go.
like i mentioned before,the battery compartment could do with some foam padding or something as the battery,once connected is free to rattle about without it.
getting onto performance,the one thing that swung it for me regarding buying the archos,is that it has a very good line out and gives suprisingly good results pugged into my denon reciever.i'm guessing this is why my sp25's have always sounded pretty good plugged straight in the headphone jack.
the one problem i did get though was listeing to some tracks in a more noisey envoirnment (as you do) which is what led me to getting the bk amp and for this reason the amp cant be faulted..loads of volume without losing any detail.
i mentioned earlier i no audiophile but like most people i can tell what sounds crap and what does'nt and the bk falls in the does'nt catagory,as mentioned in the previous posts the difference is not black and white especially as the senny sp's are a bit bassy to start with but on further listening this seems to have a bit more of a punch to it and the whole thing sounds a tadge more lively and clear even when loud (think you ears will give out before the amp!)
the results playing about with the wifes little creative muvo were more of the same but a bit more obvious.again punch and clarity along with great volume.
admittenly this is my first amp but for others considering dipping a toe i cant really see you going wrong for 30 quid (excl the £8 p&p

)