I've got X-Mini II, it's a lot more powerful than one would expect from something that's barely any bigger than an egg.

Sound quality is great, unless you connect it to something that's already powerful (i.e. your computer) and then turn the volume all the way up. The sound starts getting a bit dirty in some songs, but not all. Sitting next to it starts getting painful, because it's really loud.

The input is via the headphones jack. You can daisy-chain a bunch of these together for more sound, each one has its own headphone jack, plug and battery.

They are recharged via USB, so in worst case scenario you can just grab one of dem Backup Power Chargers which run on AA batteries. Mine is about a year old, but it still lasts for quite a while. When brand new, it lasted around 14 hours, but that wasn't on max volume.

If I lost mine, then I would definitely buy one again. It's very nice and very portable. Comes with a carrying pouch, so won't get dirty.