I purchased my 996xt two years ago and have thoroughly enjoyed this scanner. I also own the PSR-600 scanner by GRE, which I bought a year prior to my 996xt. Although I love my PSR-600, once I learned to properly use the 996xt I quickly realized if I could have one P25 scanner it would definitely be the 996xt.
The sensitivity of this scanner is quite good and I'm rather partial to having a tuning knob vs only an up/down button controller. This makes tuning around much easier than having to use traditional up/down buttons some scanner models utilize. My older analog Pro-2035 and Pro-2042 scanners also have a tuning knob and I much prefer using these scanners to tune around looking for signals.
I also own some Icom receiver gear, one among which is the IC-R8500, which is my preferred receiver for serious listening, but I must admit my 996xt scanner isn't too far behind in terms of listening pleasure. I also love the pre-programmed "Service Search" feature, as it allows for quick and easy searching for various services. Most serious scanners have this feature but the 996xt is also a pleasure to use in this regard. All the buttons are back-lit and are fully adjustable for any lighting conditions. The menu system takes some practice to learn properly but once I used it for a couple months I became a pro and am able to quickly navigate any function. Again, I can't stress enough how important it is to really use this scanner to learn it's features. Too many people have purchased this great little scanner only to become disillusioned because they felt it was simply too difficult for them to use. Practice is the key here. Using it every single day and studying the manual made learning it MUCH easier :)
This model also has a couple features not found on my PSR-600, which is Fire Tone-out monitoring, something some people have no use for but I do and it's a fine feature to have if desired. I also love the ability to add a GPS receiver to the 996xt, which makes mobile use much easier than traditional scanners. It also has greater frequency coverage than my PSR-600 and has WFM mode (again, something my PSR-600 does NOT have). Although I rarely listen to FM music using this scanner, there have been occasions where I have done so, so it's a nice feature in my opinion (although it is in fact mono only).
The display is among the best I've seen in a traditional scanner. The large, clear display is extremely useful and is but one of the reasons that attracted me to this model. Plus, it's ability to change color to the service being received at the moment is also a great feature to have. Audio output is also reasonably good. Although I rarely use the internal speakers in scanners of this type, I have not had the need to use an external speaker on my 996xt. It also has adequate connection points on the rear panel, some thing the PSR-600 is lacking in, as I had to modify my PSR-600 to add a record-out (or Line-Out) jack. This feature is included on the rear panel of the 996xt though, and rightly so because it's a necessary feature of any high-end scanner of this type.
Button layout is very good and once you learn it's operation it's very easy to use this scanner. I also liked that it came WITH programming/control software (FreeScan), something my PSR-600 was NOT provided with. The software, although somewhat basic, works extremely well and after testing several paid software for my 996xt I decided to simply use FreeScan, as it proved more than adequate for my needs. Although I haven't seen many installations using the in-dash (DIN) feature, this scanner can be mounted in this fashion, as can the PSR-600. The 996xt comes with the necessary DIN key whereas my PSR-600 does NOT.
As I stated earlier, if I could only keep ONE scanner it would definitely be the 996xt. Even though I also love my PSR-600 I simply love the added features the 996xt offers. The 996xt typically sells for more than the PSR-600 but if you have a need for the added features it's well worth it. One thing to note however, is the 996xt as well as the comparable PSR-600 can only decode APCO-25 Phase-I systems so if you want or need to monitor a P25 Phase-II system this model is NOT for you. To date, the ONLY scanner capable of decode a P25 Phase-II system is the GRE PSR-800 (also a fine scanner as well).
There are other attributes the 996xt has but this covers the vast majority of the reasons why I chose to purchase my scanner, and why I would choose it over my PSR-600 if I could only keep one of the two. I highly recommend the 996xt but only IF you have P25 Phase-I systems in your area. Do some research before buying any digital scanner because you don't want to get stuck with a scanner that won't fit the bill, especially if you happen to have a P25 Phase-II system in your listening area, or even one that is coming soon near you. Please check first BEFORE buying!