I wonder how many they're actually selling at $399 though? IMO it just isn't compelling at that price point.
I used to think that until I bought mine after briefly owning a Picoscope (and looking at other similar things in the similar price range) and honestly I think the price is justified once you begin to use it. The software is really, REALLY good and that's what the product really is* rather than the box itself (it's OK, but the lack of proper BNC connections really lets it down).
Quick example:
I bought the Picoscope in May, only to find out it didn't work for shit on Mac despite being advertised as a cross platform solution. Version 6 sucked, and version 7 was in perpetual beta with only the most basic functions sort of working. I was assured that the stable release was coming in September, October at the latest. I could wait, or I could send it back. We're now in December and it's still not done so I'm glad I chose the latter option.
On the other hand, a while back I was setting up the function generator on the AD2 and thought it was annoying that you could only set output level in peak amplitude. I sent them a quick note asking if there was any chance in future they could add an RMS option there. I think it was less than 24 hours later I got a response with a link to a beta update where you could now choose from 6 different output level units. They're THAT responsive.
The software has been rock solid for me, it's laid out really well and it's incredibly powerful. Of course I'd have loved if it was cheaper when I bought it (I hunted and the best deal I could get was nearly $600 thanks to Australia tax), but in practice $600 for a perpetual license bit of software* that kicks ass seems OK to me. I pay something like that per year for Fusion 360 and that sucks ass.
* Yes, I realise the software is actually free and will work with sound cards and stuff like that. I'm not literally saying the software costs that much, of course you get the box for that price, just that the software is WORTH that much as a lab tool.