I received my shipment of DTQ450x today, spot checked a few, and verified that they are reading just as accurately as the one I bought in 2010/2011. I also brought in the TCCT model which is the kitchen style remote probe with built in timer and set temp alarms. Here's the limited data set for those two and how they stack up against the thermapen.
Keep in mind that I'm 98' above sea level so true boil temp is 211.8F. The error data is measured against 212F before I figured out my elevation.
Some notes on the data... Ice Slurry is filling a cup all the way to the brim with crushed ice and then filling it with water. Stir the slurry with the probe keeping it in the center of the mass.
Boiling is a rolling boil with the probe not touching the bottom of the pot.
The mid point "error" for the CDNs are as compared with the thermapen. Of course they can all be reading a little off here but I felt this data was useful since everyone considers the thermapen to be the holy grail.
Summary: DTQ450x is about 1-2 seconds slower than the TP, but only when making huge swings of nearly 100F. For our purposes, they are equal in read speed. Accuracy at ice and boiling are good and it tracks almost perfectly with the TP in the mash/sparge ranges.
The big surprise was the TCCT. I picked this up as a goof to see how bad it would be since most people have thrown a few of this type away. I always liked this style since they have a timer built in and most importantly that it had temperature alarms so that it tells you that you're about to overshoot your strike water temp. I'm pretty sure it also has a low temp alarm so you can make sure to add some heat to your mash when it drops too low.
The surprise was how accurate it was. Yes, it takes up to 30 seconds to find the actual temp, but again, instant read isn't really that important with brewing. At this price point, I'll take accuracy over speed. I haven't added this to the site yet but it's going to be about $19.