The Studer A721 is a tape cassette deck that I have used for transferring cassette tapes over to digital form.  However, this was intended for other use when it was made, but since no one really uses cassettes anymore, it is now most useful for transferring old tapes into digital audio.  I have this hooked up to a Pro Tools HD rig via a patch bay and we use it at the studio solely for transfers.  The unit has served us well for transferring tapes and definitely does its job well, but it is quite limited in its use and really only comes in handy once and a while.  The Studer A721 isn't hard to set up and everything about it is pretty user friendly.  There are a decent amount of buttons and parameters, but the typical functions are easy to find and operate.  I can really only speak about using this as a device for transferring cassette tapes to a digital means because I really don't have any experience with using it for anything else, which isn't to say that it couldn't be used for other things, I just have no use for it otherwise.  Since these are obviously no longer made, they are somewhat hard to come by, but won't cost all that much if you can find this particular model.  There are a few other models of the Studer tape deck like the A710 which I probably like better overall because it is designed better in my opinion.  If you are looking for something to transfer cassette tapes, this will definitely do the job and is definitely okay for simply listening to tapes, but I wouldn't recommend expecting to get anything else out of the Studer A721.  Overall, this is a machine that will die out in the coming years but does still serve a purpose.