As one of the earliest adopters of the DTR (and now DLR series) I can weigh in on the mobile antenna issue. I have tried several, all tuned to the 900MHz band, and NONE of them have worked well. I did some range tests with several DTRs in a vehicle inside a garage; one with a mobile antenna on the roof; one with a long stubby and one with the short stubby. The factory stubby antennas always beat the mobile one by a substantial amount.
At the time, I speculated that at those frequencies, the loss from the cable exceeded the gain from a ground-plane antenna outside the vehicle.
It's easy to do back-to-back tests like this because you can set several radios to different hopsets and then try calling them using the PTT. You don't need to record the response or have a friend at the other end; you can tell as soon as you push the PTT if the other radio is in range or not.
Incidentally, the short stubby and the long stubby were almost identical in range, and the DLR series with the fixed antenna was not much shorter.
While results will vary depending on a lot of location factors and one can't extrapolate results from my own tests, it was quasi-scientific because I tested them back-to-back. I was in a neighborhood with a lot of mature trees and old buildings, where GMRS and Part 90 radios would give me about 4 blocks maximum, the DTRs with the long stubby gave me about 8 blocks; the short stubby was about 7 1/2 blocks, and the DLR about 7 blocks. That is amazing coverage.
With the mobile antennas on the receiving radio, I was lucky to be able to get 2 blocks away before it lost the signal.
I also found out that the body is a great absorber of RF signals as we all know, but the DTRs seemed to be just as good on my belt no matter which way I faced, but the Part 90 (450-460 MHz band) would drop the signal suddenly, simply by placing my body between the receiving antenna and the transmitting antenna. But the 900MHz radios don't refute the laws of physics and must still be within line-of-sight, so if I didn't get a return signal when on my waist at the fringes of my range tests, simply raising the radio above my head would add another 1/4 block.
Lots of fun. Sadly, they no longer fit my needs, and I am going to miss their quality, clarity, battery life and range