I've had a pair of these speakers for a good 10 years now, and have travelled all over with me, and they're still going strong. For passive sepakers, they're very good. Fairly light as they've got no internal power source. Basically, they're just a bigger version of a pair of headphones. But I really like them.
The cons are really that the sound quality isn't perfect, and the volume level isn't huge - obviously depends on the volume of your walkman/iPod etc... But if you're aware of this in advance, then you don't expect it. They're also not the smallest of possible speakers that you could take away with you, but they're not an awkward shape and are easier to pack than you think.
I pack them away with my luggage when they're travelling - when clipped together at the base of each speaker, I can wind the cable round the middle, and it fits quite well there. They are very durable, and can take being wedged down the side of your bag, or on top of everything and lugged around on public transport, or on planes. They always come away with me, and there's barely even a scratch on the surface.
They're perfect if you're staying in a hotel room, or a hostel, or even an apartment. They're probably not good if you're planning on using them outside, say on the beach or something as the sound won't carry too far.
If you want something cheap, durable and very reliable, then these are perfect. Highly recommended.