Have been using SDR's for a long while now, as well as software defined military radios. Wat made me break into the amateur side was finding out that Icom was supplying the first few "black box" receivers for the Predator (RQ-1, surveillance only, no Hellfire missiles back then) fleet. The civilian versions of the PCR-1000 had some issues, like being able to be opened up like those purchased for military/export use.
Now, like others have mentioned, I monitor my own networks with SDR receivers, and the HackRF is better than the cheaper USB versions, but it is so easy to just carry along a small USB/antenna and listen to what is nearby. For portability, I used a re-purposed Hinge Health Amazon Fire tablet and SDR# with USB dongle. For the money, great combination and makes the tablet useful again. My newest "scanner" would be a Uniden BCT-15X (possibly a handheld Uniden floating around somewhere), as the SDR USB sticks are on every older computer now, doing something at some point.