The Groove Tubes PDI (Passive Direct Box) is an affordable DI box that can be used in any way that you'd like. I've used the box in a professional recording studio, mostly to record keyboards, but it can definitely be used for live shows as well. The box doesn't require any power or anything since it is a passive box, and has 1/4" connections for both input and output, as well as a balanced XLR output. It isn't rack mountable in any way.
Using the Groove Tubes PDI Passive Direct Box is incredibly easy. If you've at all familiar with DI boxes and have used any other model in any way, you won't have a problem adjusting to using this one. It isn't like you need to do anything once you've made your connections, as it simply has a ground switch and nothing else in terms of parameters. I don't believe that manual is at all necessary for this DI box.
While perhaps not my favorite sounding direct input box out there on the market, the Groove Tubes PDI Passive Direct Box still does have a pretty good sound and will get the job done more times than not. It won't color your sound or anything like that, as it pretty much will throw back at you what you send it as far as I can tell. I've used the PDI for recording a few different types of keyboards, including a direct out from a Fender Rhodes as well as a modern digital keyboard. Although I can't say I have further experience using the PDI for other applications, but I would think that it would translate to anything you'd want to use it for, as it isn't like you have parameters to set that could change it one way or the other. Basically what you've got is what it is and there isn't any room for changing it...
For an inexpensive direct input box, the Groove Tubes PDI Passive Direct Box is a great way to go. While not as versatile in terms of parameters or as clean sounding as some of the upper end DI boxes out there, for boxes in this price range you're getting a very good sounding piece of gear. While I'd probably recommend these mostly for home studio owners or those on a budget, this is definitley suitable in a professional environment as well...