AFAIK, the Demeter is the only tube DI which sends a tube buffered signal to the parallel unbal. line out as well as the bal. xlr out. The Brick only uses the tube stage for the bal. line (the parallel out is simply a "thru"), and I believe the REDDI does the same. Yet, that being said, the REDDI has much more of a tube/amp sound at its' output.
I also believe, but may be wrong, that DB900's unbal. output is not buffered by the tube stage (altho, that design is somewhat copied from the Demeter VTDB).
I have tried the ART stuff...and while some folks do rave about the "tube warmth" (geez, what an overused term there...) these impart, I have found that while there is some tube character it is minimal. The tube recieves very little voltage, is placed down the signal path (following a bunch of ICs, and followed by a bunch more), and the unitys are, for my ears, too noisy.
The U5 is SS.....and one of the finer SS devices you will find. It is clean, warm, and exceptionally high quality. Unfortanately, it is also big and bulky...and hence mine stays at home.
I am VERY happy with the Demeter. With a 27 megOhm input impedence, there is NO loading or compromising of the signal whatsoever. The unit is dead quiet (the VTDB is my studio rig....), rich, warm and detailed sound from both the bal. and unbal outs. Built like a tank as well. I have changed out to different tubes a few times in mine. One (I have two of these...one an old model from the late 80s and one a new model...sound the same, same components and build quality) now sports a NOS Mullard while the other has a NOS JAN GE Large Plate.....
I actually use one as an input buffer for piezo equipped basses (Turner Rens). works wonders with a rich and detailed tube sound.
They are pricey, but well worth it. Quite comparable in quality...not tone...to a U5, ADL, Manley but loads more portable!
If price is no object, tho.....look into an Evil Twin by Eclair Engineering.
And, after trying one, I am very interested in a REDDI.
Max