I thought I'd write a bit more about the Zoom H4, which does look like something you would use to subdue an assailant with an electric shock. I've yet to have anyone ask me if it's a weapon, but haven't tried taking through an airport in hand luggage.
I bought the H4 when I was trying to expand my options for recording beyond what I could plug into the PC soundcard aux input. I didn't own any decent microphones, so couldn't do any vocal or acoustic recording. I also wanted to be able to record in other locations such as the African drumming group I used go to and some of the concerts my kids play at.
There are some other similar devices out there, but I went for the H4 as you could record either with the built-in in microphones or plug in a guitar and have some effects to use. I never owned a 4-track cassette multi-track, but this is a modern equivalent. You can do most of the same things, including bouncing tracks to get more effective tracks, but I have only done basic stuff in that area. I have done lots of field recordings and the quality has been generally good from that, although you have to make sure you set the correct levels. Loud bands require low gain. I've only once recorded at a professional gig, but that was a small venue where I had the permission of the band. I've not tried sneaking it into any big gigs, but it's quite bulky and tricky to hide.
As an audio interface it is plug and play with Linux. You get prompted whether it should act as a card reader or an interface. It's only USB 1.1, and so limited on transfer speed. As with most such devices you only get 16 bit stereo at either 44.1 or 48kHz. In standalone mode it will do up to 24 bit at 96kHz, but I've not used that mode. I didn't initially realise that you can also play sound from the PC through it, but that means you can do all monitoring from the headphones on the H4.
There are a variety of effects built in as found on other Zoom devices. These are perfectly adequate for practice and demos. One of the downsides of the H4 is that the controls are quite fiddly. You have a joystick on the front and a small wheel on the side that do all navigation. Just tweaking a setting on an effect requires lots of operations. Entering names for tracks and effects is done in the same way. You can apply some modeling to the microphones that is supposed to simulate some classic microphones. This is something else I haven't tried, but ought to run some tests.
For many application you will want to mount the H4 on some sort of stand. It comes with a cover that you strap on with velcro and has a standard camera tripod threaded hole. I've used this with a GorillaPod in various locations. When recording at home a normal microphone stand is more versatile, but the only adaptor I've seen to convert between the two types of thread is by Roland and relatively expensive. I eventually worked around this using a very cheap (£1) tabletop tripod and some tape. I plan to get an 'anglepoise' type stand that I can clamp to the desk. I should be able to attach to that in the same way.
Since I got my new audio interface I've continued to use the H4 as my microphones. You have to hit the record button to get audio (in paused mode) via the line out. I tried running it with USB power, but got some extra noise that way, so am using batteries (rechargeable of course).
I'd recommend the H4 if you have similar needs to me. As there are newer models that do more you can probably get one for a good price now.
I created a page for the H4 on the Linux Musicians wiki. Perhaps others will add useful information there.