Hey CZ -- (Btw, is your username a reference to the line of detectors? Or do you really like fake stones?

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Things I don't love: As is often the case with people, their strengths are also often their weaknesses. In my experience, this has translated into a longer learning curve for me relative to any other detector I've used.
* Flexibility/programmability: The fact that so many things can be changed in so many ways, and there are interactions with some of the parameters, can cause pain, particularly early in the process. Many will say "just start with one of the preset programs and learn the basics". I did, and was initially very unhappy. Which then leads you to start screwing around in potentially random (and potentially counterproductive!) ways. I'm not kissing a$$, but Andy's book is very helpful with respect to better understanding what to adjust, when, why, and how it might impact other settings.
* Design choices: Similar to above, but (again -- for me -- so this is subjective) XP's choices to make this a relevant and valuable detector in the US and Europe means that they aren't catering to a US user's needs. I get it, but I think that contributed to some of my early difficulties with the presets. Almost ALL of my local hunting is done in trashy parks -- and trash as in pulltabs and bottlecaps rather than iron, though that certainly exists in some parks as well -- so it took some tweaking to get it really humming. Another choice is that for deep targets, as Andy puts it, rather than "guess" at what the target might be, the Deus may not show a target value. You can use other tools to try to assess whether you want to dig. But for some, that is a "flaw". For me, it made it harder early on to understand what it was saying, and what I might do about it.
I could go on, but I think you get the picture. Once you learn to harness the potential & power of this detector, I suspect that you will love it. And while it "just clicks" for some users early on, my highly unscientific anecdotal observation is that it seems to take some time and effort for many, and some folks seem to give up on it rather than invest the time & energy. Right now, I feel like I've learned how to drive a standard transmission after having driven automatic all my life. I'm at the point where I'm no longer burning out clutches, but I'm certainly not yet maximizing the horsepower, transmission, and handling this puppy is capable of!

At this point, when I struggle with it, I still believe it is due to my lack of understanding/experience rather than a true shortfall of the detector itself.
Just guessing, but I'd say that 90% of what I've found with the Deus I would have found with another one of my detectors, and in ~20% of the cases, it might have been easier to find with another detector (less time trying to discern what the Deus is really saying). BUT, I know that I'm also digging a lot fewer bottle caps (once I figured it out!) with the Deus than I would with my other detectors. And as I continue to understand and trust the Deus I suspect that the 20% will tail off to near zero.
Annoying things? They are small. Perhaps even petty of me to point out. I find that dirt/grass seem to get into the coil cover easier than some of my other detectors. So I have to remove the coil cover more frequently to clean it out. That leads me to believe that I'll need to get an extra coil cover NOW because you'll notice that the coil cover has the clip guides (and spacing!) needed to charge the coil. Yes, I should just consider it part of the cost of ownership, but it feels annoying to have to have an extra charging clip, an extra coil cover, etc. to ensure I can use the detector without interruption. The rubber cover on the controller (for the charging input and wired headphones) seems to pop open too easily. Told you it was all petty.
And to be clear, I love my Deus, and there are so many things to love about it.
Take care,
Rich