One consideration I didn't know about when I got into it -- from RSPduo's site "both tuners can operate simultaneously anywhere between 1kHz and 2GHz with up to 2MHz of bandwidth per tuner"
Well. That's good and 4Mhz of bandwidth may be enough for the location of interest, but for a really busy large metro trunking system, you might need 8Mhz or more to cover all the frequencies of interest. It depends on what you are trying to do. For one of my locations on a p25 phase 1, I need a bit more than 10Mhz to be able to capture everything. So, that works out to either buying two AirSpy Mini's (8Mhz bandwidth each), or pushing at least Four RTL-SDR's (~2Mhz each) and fudging/pushing the center frequencies a bit on either end with sample rates -- and I might miss a high and low end frequency or two resulting in missed conversations from time to time (five would be better).
Granted, I'm not just listening live, I'm recording for later review with trunk-recorder, and playing back with either rdio-scanner (live) or trunk-player (for review). You'd also be using Linux for that -- or running a Linux virtual machine on windows (VirtualBox). Setup is a bit harder, but it's more of what I wanted to do and it's easier to customize talkgroups......well, at least for me.