Well, I was able to get it running on Windoze using SDR Console V2.2 (the olde V1.5 will NOT work), and SDR#.
No joy with HDSDR, at least not with any of the DLL's I tried, and I'm not about to risk trashing my Windows PC by trying to get GNURadio to run on it.
And I was finally able to get it to run on Gqrx on my Linux box by removing, and then reinstalling, Gqrx. Gqrx uses a block of code (gr-osmosdr) to communicate with the device, and if that code isn't on your machine when you install Gqrx, it won't detect and use it if you install it after Gqrx.
Once I did the "RnR" to Gqrx, the HackRF showed up in the list of drivers to use, and it's running happily right now, and I'm listening to KLOS with it.
The more I delve into the documentation (what there is of it), the more I realize that the only way you'll be able to make this little puppy sit up and shake, and roll over and bark, is to use it with GNURadio. ALL of the "Plug and Play" software out there treats it pretty much the same as a "$10 USB Dongle", and can't take advantage of the flexibility of what GNURadio can do with it.
And it's still just an 8-bit receiver, like a $10 dongle, even though it can generate some RF as a transmitter. Read the link to get a basic understanding of 8, 12, or 16-bits in this context.
Is it worth $300?
That's a tough question to answer. If you want something to plug-and-play, then you're probably better off with a $10 dongle, or one of the better ones available out there. It will plug right in to a Windows or Linux PC, and work with minimum effort.
If you have the time to spend to learn how to set up a GNURadio "definition", AND you understand what you want to do, then this might be for you.
And if you're really serious about a DIY SDR for whatever purpose, you'll find other choices out there that may suit your intended use better.
I haven't decided yet if I'll keep this little guy, or eBay it. I don't really need it for anything I'm doing, but it's a great platform to learn GNURadio on.