I broke down and used some tax $ to buy a PRO-97, primarily for the Signal Stalker II feature, but also just to have another portable around, especially one with MilAir capability.
One thing you need to understand with nearfield reception (Signal Stalker, Close Call, Signal Stalker II, Opto Scout, Opto Explorer, etc) is that the signal you're capturing normally has to be significantly stronger than all other signals in the area. For example, if you're near an "antenna farm" where several strong paging transmitters are located, it's not likely you're going to hear much. This is very simply put but is simply the case. Sometimes less is more. You speak of using an external antenna to try to capture unknowns, but sometimes this can backfire on you, again depending on where you are in relation to strong transmitters.
You are also sacrificing reception distance for speed. These devices blow through the spectrum at a very high rate of speed, and as a result are only hearing the strongest of signals. It's a matter of location and timing.
I have a 246T also, and while I have not done a side by side comparison yet between it and the PRO-97, I can tell you that Signal Stalker II has at least for me worked better than the Close Call feature of the 246T. I have run both while mobile, on the same trip to/from work 5 days a week. The 97 has already found a great deal more than the 246T did. I have also owned a Scout and an Xplorer. The Scout was by far the fastest of them all, but without a second receiver capable of being reaction tuned you can't hear the audio. The Xplorer at $700 was a nice device but it was large and the audio quality left a lot to be desired. Both Uniden and GRE have really done a nice job with their early offerings of this feature IMHO. Scannists getting involved in this type of reception for the first time simply need to understand that it is a far cry from the normal scanning they're used to doing. In this case a lot of times less can produce a lot more. Your mileage may vary.