Although I have no experience of any kind using an IQ3, I do have considerable experience using external HDMI monitors in the field with my various FrankenKamera outfits. For example, here's a photo of a 4k, 12.5" Lilliput A12 being used with my Cambo WDS-based FrankenKamera outfit:
In addition to the A12, I also have a 2K 7" Apture VS-1FineHD I use when I need my camera outfit to be smaller and lighter and more portable, as it weighs just under 1 lb, whereas the A12 weighs ~2.5 lbs.
A few observations based on my experience to date:
1) The larger the screen, the greater the benefit there is from using an external HDMI monitor. Except when it comes to carrying the combo around over my shoulder, which is why I ended up with two monitors instead of one, and switch between them as appropriate.
2) When it comes to choosing a monitor, specs alone do
not tell the whole story and price matters less than you might expect. Although I ultimately ended up with two monitors, I actually tested at least a half-dozen others, including two that each cost more than $1k and both of which didn't work as well for my purposes as the two I finally chose.
3) Most monitors are aimed primarily at videography, not photography, hence many (or in my case, most) of the features they include are likely to be superfluous. That said, it's pretty cool to be able flip the image upside-down and reverse it left-to-right to achieve a proper view-camera experience whenever you're in the mood for one.
4) If you plan to photograph in both horizontal and vertical orientation, then (IMO) it's essential to have some way to rotate the monitor, otherwise much of the benefit of using an external monitor will be lost. In my case, I fabricated a lightweight, rotating monitor mounting bracket from an aluminum step-down ring and scraps of carbon fiber sheet and various screws already on hand, but other options are available (albeit ones that are typically larger, heavier and/or more expensive.) And as I later learned, adding a safety strap to the monitor is a good idea, too, in case it gets snagged by an errant tree branch when you're hiking with your camera and gravity succeeds in pulling it away from its mounting bracket and all the way to the ground.
5) If you can swing it, using an external battery pack to power the monitor via an external power jack is a better choice than using camera batteries that mount on the back of it. I'm able to use just one external battery pack to power both my camera and monitor and I've found this makes life much easier when working in the field than trying to keep track of two batteries and having to swap them out every 30-45 minutes or so.
6) Screen glare can be a significant issue for daytime photography and most OEM hoods aren't as effective as you might hope. Fortunately, I photograph mostly at night, so this isn't a huge issue for me, but when I do photograph during the day, I use an aftermarket hood that completely seals the screen from outside light, otherwise the monitor would be much more difficult to use under our bright, Arizona skies.
And with all of that said, as helpful as working with a monitor can be at times, I now find myself leaving them at home as often as not. Because I photograph mostly on foot -- no "drive-by shooting" for me, thank you! -- and after a walking several miles over the course of an outing, every ounce of weight I carry seems to matter more than it did even in the recent past. I have successfully whittled the weight of my custom camera / tripod / lens combo to well under 7 lbs. and even adding just a single pound by including a 7" monitor sometimes just isn't worth it.
Anyway, free advice is, at best, worth what you pay for it -- especially when it originates with me! -- and I wish you great success with your project!