Sound Devices MixPre-6 II

It's small, and designed for field use, which means there's some compromises that have to be made just in order to fit so much on such a small device.

Especially in terms of powering solutions, I am not a fan of AA batteries, and I'm not going to pay the asking price for a plastic sled to mount Sony batteries either.
You get very good operation times with just about any USB charge pack however, in my experience.
A 5V 1Amp pack is only able to power 2 preamps at the time, that's still plenty for my needs in most situations as I can still use the other inputs for line-in for instruments, etc.
My 10400mAh USB charge pack which delivers 2.1A for tablets etc. fully powers this for hours, should I need more microphones, and you get much larger capacity packs.

My only concern then is the USB-C prone to wear and tear, but it's somewhat protected by the XLR plugs going into channel 1-2, so I'm not too concerned powering it like this for now, but I'll want to invest in a bag with internal frame to protect it better and I'll fix a cable to the frame so it doesn't accidentally pull on the socket of the unit.

Overall I think they have done a great job in terms of fitting so much versatility and features into such a small device, and the quality is overall superb.
It's really well built, sounds crystal clear, very nice preamps.
Operation is intuitive and well thought through, the touch screen is very snappy. Very flexible in terms of various use scenarios. It's clear that Sound Devices have put a lot of thought into this.

Very happy with it, I'll be carrying it everywhere.

This is professional, high quality and very compact device. I've been working with different hardware for a long time but I feel that I made my next with this one. I'm sound designer and I use to work doing field recording and processing and mixing sound in the studio. The Sound Device Mixpre 6 II allows with no complications move from home to outside with no problem, in a handy way and not bringing so much weight. One of the things that I really like of the second generation of Sound Device is that allows to record up to 32/192 giving me the option to transform more the sound without losing quality.

It's small, the material quality feels sturdy and made for if it gets busy and hectic on set. With a proper V-Mount battery and a boom mic that always requires phantom power you get super long battery life.
With the recorder being small the touch screen and knobs are as well, you have to get used to that a little bit.
I think a good interface for a fast workflow is super important when it gets busy and this device excels at that. Having those 4 mic pre combo inputs at real 32bit conversion at that price is amazing.

That being said if you want to use a v-mount battery you need to buy the v-mount holder extra. It's quality is bad and it is extremely overpriced in my opinion, but since this is the review of the recorder itself it still gets 5 stars from me. Just be warned.

I have a few observations, as I have been a long-time user of the Tascam Portacapture X8:

The Wingman App allows me to start and stop recordings nicely, but I don’t see an option to play back recorded files using the app!? Is this really not possible? I would love to be able to navigate and listen to my recordings using my phone or iPad! With Tascam, this is not an issue at all, but here I have to go through the menus manually, which is quite inconvenient.
Addition: Yes, this is a problem, especially since I cannot play back 32-bit depth files and have to use a computer for that.

Another thing—Solo monitoring is still unclear to me. Is this something that cannot be done using the Wingman App?
Addition: Yes, but I got around it by using Star Button Menu → System → Star Shortcut and selecting Mute/Solo.

And one more observation: The XLR inputs are labeled 1, 2, 3, 4, but these don’t match the corresponding buttons! If I pan channel 1 to the left and channel 2 to the right, I actually have to do it the other way around because channel 1 is actually channel 2 and vice versa! How is this for others? Or do I somehow have my cables connected the wrong way inside my device?
Addition: Not a problem, solved!

The sound quality and Headphone Out is superb!

After reading other users' comments, I initially couldn't believe it was this bad, but I ended up ordering the following on the same day:

Sound Devices MX-LMount
2x SupraCell Sony NP-F970 batteries
A dual charger for these (SONY NP-F970 Dual)
Since I plan to do field recordings where no 220V power supply is available, I need a reliable power source that lasts at least 3 hours!
Addition: such batteries were a small overkill, but I am pleased.