I have these boards. They are great!
This is what mine look like:
So, the parts-- I didn't populate any of the internal parts, I am just using the traces from the 2mm holes to the 2.54mm holes. So far so good.
The parts I did solder in were 2mm headers sourced from Amazon which just came in handy. And stacking 2.54mm headers also from Amazon. I used smaller ones and had to sand the ends to get them end to end (I used a 10 & a 4 on one side and two 6 hole headers on the other. You have to sand between or else there is too much plastic between them). Buy the longer ones from Adafruit and trim one side(no sanding).
When checking your conductivity and verifying 0 ohms between the Omega Pins and the stacking header pins-- realize that the power pins are at a 45 degree angle and you'll have to look at the diagram. After that all the pins are nicely labeled by the silk screening on the PCB depending on how good your eye sight is.
Go light on the solder so you don't have it bleed into the stacking header socket side.
Lastly it is a tight fit all around. The Omega 2 barely fits in between the stacking headers. Then when you get it assembled, the whole thing doesn't fit as well as one might hope into the breadboard-- the headers on top come in awful handy.
It made it so easy to hook up, I fried it with 5V before I knew it! But seriously, the boards from PCBs.io are pretty good and this is what I did with a couple of mine...