The Explorer came out a year ago. At the time, there were very few comparable options. The iFi iDAC was the most similar on paper, 192 kHz for $300 (and of British make, for what that's worth) but availability was even flakier than Explorer. The Dragonfly was $50 less and more compact but capped at 96 kHz. The base Bifrost was $50 more but had no USB (effectively capped at 96 kHz) and wasn't portable.
Stands to reason that more compelling price/performance propositions have emerged in a year's time, especially since DAC product development is evolving relatively briskly, but the Explorer still holds its own at $300. It sells for more than $200 on eBay, which is a respectably small used discount.
You can go cheaper or more expensive, but there are still not many alternatives at $300. There is the hiFace. Herus also offers more features and appears to be a good value, but it is $50 more. With these new options, if you're not playing music sampled higher than 192 kHz, you could make the argument that you're investing in capability you don't need, even at the desired price (although you could also assume you're getting better technology that inherently has the richer feature set that you can't carve out). The v2 Dragonfly and the Microstreamer are much cheaper at $150 and $170, but still no 192 kHz.
If I were purchasing now instead of last year, I'd be looking harder at the cheaper 96 kHz units or something non-portable closer to $500. I decided to take a 192 kHz plunge then, and would likely do it again, but it might have been nice to cap the sample rate at 96 kHz to afford more music for the money. And I wonder whether I really get enough out of the higher sampling rate, day to day, to justify it. I also rarely exploit portability, so I might opt for a fully loaded Bifrost or something. That contradicts my doubts about whether the 192 kHz capability is worth it, but maybe throwing a little more DAC at it would sweeten the proposition (put another way, maybe a $300 DAC doesn't do > 96 kHz justice). And part of my reasoning for investing in 192 kHz transcends my day to day listening—if I'm going to buy a classic recording again, I want to get the best practical version.
So, purchasing now instead of last year, I might still wind up with the Explorer.