The Whirlwind MultiDirector is a simple four channel passive direct input box. Each of the four channels has a 1/4" input/output and an XLR output. Each also has a pad and a ground lift switch. The whole unit will fit in a single space on a traditional rack casing, which is pretty impressive considering there are four DI boxes in here.
Setting up and using direct input boxes in general is very simple, and the Whirlwind MultiDirector is no exception. There isn't anything complicated about it at all as everything is self explanatory. Even if you don't have much experience in the studio, this is about as simple as a piece of gear can be, so I don't believe that manual is necessary.
In my use of the Whirlwind MultiDirector, I've found it to do nothing but give a faithful reproduction of what I send into it. I've used it a couple of times for a few different applications including electric guitar, bass guitar, and keyboard. For all three applications I was very pleased with the results, as I don't think that I could have asked for too much more. This is really as good sounding as most of the other DI boxes that I've used.
I really have no complaints about the Whirlwind MultiDirector. For those who are doing large sessions where you'd need four DI boxes at once, this is really the perfect unit. I've used other DI boxes with more features for sure, but this isn't a bother here considering that you're getting four of them in one unit. I don't think that I've ever used all four of these in one session, but I've used at least three of them at once and I know that the studio where I used it does end up using all four often. The price is very reasonable, especially when you break it down to price per DI. If you need four DI boxes, there's no reason to buy them individually when you can get the MultiDirector for a fraction of the price.