There are many DI units on the market. In the studio we use "Radial" DI and Reamp units. They're a bit more expensive than the usual DI. They're also phantom powered. We also have some passive DI boxes, but I can't remember the manufacturer. A DI box isn't much bigger than the "plug" in your post, so I don't get all the hype about it's size. In the studio we find that plugs like this don't last very long, but they do get heavy use. (They loosen up and start causing connection issues. At least the ones we had did.)

Also interesting is that the plug on that site appears to have a TS 1/4". This would mean that, as a DI, that plug is completely worthless in a studio environment. It may match impedance, but it doesn't provide a balanced circuit. This would limit its application to directly plugging into a console. In the studio we often have cable runs of 20+ feet. Cable runs longer than 10 feet can pick up a lot of noise and interference. Using a 5 foot guitar cable, plugged into one of our DI boxes means that only 5 feet can pick up noise and interference. The DI box provides a balanced, low z signal, that doesn't have noise/interference problems so can be run 100+ feet if necessary while retaining the full signal without any extraneous noise or interference.

Be aware that if you connect a balanced line to an unbalanced piece of equipment you no longer have a balanced line so noise and interference will still be an issue. A balanced circuit requires ALL connections to be balanced from the initial balanced point, (the output of the DI,) to the final balanced point, usually the console. If there are any unbalanced connections anywhere in the signal path the entire signal path will be unbalanced.

Radials are great! I use the passive one for my live acoustic stuff when there's no room for a mic.

Another one that's massively more expensive, but gets fantastic reviews, is the Avalon U-5. John Mayer and Geddy Lee are two guys who talk about them and they have nothing but good things to say.

The Palmer units are great, so's the "Motherload"...

Crap. Shane, I -1'd you. Oops. I'll make it up, I promise. Damn big fingers on my laptop...#$%#$@!

Same for me. I can type like lightening when no one is watching. As soon as someone looks at what I'm doing, I appear to lose all my skills, forget UNIX commands and application details. Never happens on the phone, just when someone is watching me work. Weird, because it doesn't happen with guitar and I'm as comfortable with what I do at work as I am playing.

Thanks Xark. Yep, I'm fumble fingered as hell when people are watching... It's a bit nasty, actually...