Well, think about it: a highly specialized tuning circuit coupled with highly specialized firmware (the actual physical scanner) vs a device designed originally for pulling in terrestrial digital television broadcasts that just happens to function as a wideband radio receiver that then requires specialized software to make use of those radio signals it's pulling in.
We all are well aware that an actual dedicated scanner is superior to most any "cheap USB TV tuner" aka SDR dongles/sticks/plugs/whatever you want to call 'em. That's not to say that using such dongles or sticks doesn't have a purpose and some major benefits as well: they're super ultra cheap by comparison with a dedicated scanner, and they can typically end up doing more overall easier than using a dedicated scanner - an example of this aspect is with SDR sticks you plug 'em in, install drivers, load SDR software and potentially something like DSD+ and bam, instant digital modes monitoring without much else required.
A dedicated scanner? Unless it can feed raw discriminator output natively then you're gonna have to crack it open and find the tap point, do the soldering job (some folks use micro-alligator clips if the circuit allows it) and go from there. You risk destroying the scanner if something goes wrong during that process and I for one know for a fact that does happen.
But it's pretty obvious a dedicated device like a physical scanner will have a tuning circuit that is vastly superior to what you'll find in most any SDR dongle of any kind. That's not to say more developed SDR hardware - not the sticks - like Airspy and SDRplay/RSP or HackRF and BladeRF won't trounce a physical scanner on potential specs too.
You get what you pay for, I suppose, but I'm extremely pleased with the performance I've experienced using the two RTL-based NooElec sticks I own. I just made a post earlier today commenting on how I consider it pretty much the best $20 I've ever spent in this hobby over the past oh, 40 years or so. They're truly amazing little devices and things are just going to get better as time passes. I have had zero issues with any tuning capabilities for digital modes like P25 Phase I and II, DMR, NXDN, and so on using these sticks, nothing but excellent performance overall and I'm very happy with them. Sure I'd love to have an SDRplay and that's next on the list of big purchases but I can wait.
