I've only know of a few cases of Delta Tau being used. I have never used them myself. I haven't heard anything bad about the. They worked and did what they were supposed to do. Though there were some vague comments about programming. Overall from what I've heard, I would say they are okay.
No doubt, someone on here has used them, and you can argue with experience.
I never liked them myself, but that is more due to the design appearence of some of their other products and I just don't like their name. But then, thats just me.
best regards......casey