Summary:
I agree that this is a cost-effective upgrade, especially for a mediocre transport. I had been using my Arcam Alpha 1 as a transport to an MSB Link Dac. The DTI-Plus significantly cleaned up the sound, added more space and detail. These are available second hand for about the cost of good pair of running shoes. I considered investing more in anti-jitter, but did not think my transport merited it. I would imagine a better transport would have a better output section in any case. However, this works as cheap tweak.

Summary:
The DTI+ is a very simple, small black box. The digital signal goes in, and it comes out again. Usual placement is between the CD transport and DAC. I use it with an AA DDS II and an AA DITB. The improvement is more noticeable with some CD's than with others, but overall it represents a significant upgrade over the DAC alone. The most obvious sonic benefit is the removal of the etched, harsh glare often associated with less than perfect CD's and CD players. The sound is typically sweeter, and imaging is improved.The effect is quite subtle on most CD's, on the same order of magnitude as other CD 'tweaks' like putting the transport on a good vibration-isolation stand. Still, I'd say it was worth what I paid for it (200 $can).