To add to what Chickenhawk said, they are solid radios, with great performance for radios in their class and a greater measure of security with communications within an organization because they use Field Hopping Spread Spectrun (FHSS) technology rather than straight voice transmission over the air.
Having said this, there are a couple of things to note. As you pointed out, the DTR650 was discontinued a couple of years ago. The good news is that it was replaced with the Motorola DTR600 and DTR700, with some tweaks that further enhance this series. Both are also compatible with the DTR650. This short video explains the differences between the two models.
The other thing to be aware of is that the DTR and other 900MHz digital radios are limited by the FCC to 1 watt of power. This may seem too low, but on 900Mhz ultra high frequencies, this can get you pretty far, especially when working in buildings. This is also comparable to the transmit power of the average cell phone.
In addition, there is also a “repeater” type device available called the DRX Digital Range Extender to further maximize the range of these radios. While a bit pricey, it seems to work pretty well.