When I set out to make my own window vent I focused on a few key areas:

Version 1:

1.) I wanted it to be as safe as possible. The overlap on the window is 3/4 of an inch as well as the tab that inserts into the door frame. The entire depth of the vent is roughly .4". The two piece (sandwiched) design uses 16 M3 allen bolts, with nylon stainless steel nuts that face out of the van. This means someone can't just walk up and dismantle them. The other design choice I went with, was keeping the vent spacing large so the product is more sturdy.
2.) I wanted it to be as maintainable as possible. The two piece design makes it so that you can change out screens as well as replace the tab if it breaks. I ship every window pair with no-see-um screen installed but it can also be swapped out with a normal screen.
3.) Since it's on the outside of the van, I didn't want it to look like a DIY piece and so I set out to figure out how to make both sides have the carbon texture you see. The two piece design helped me achieve that.
4.) The left/right piece design allows you to store it in the door when not used. The left/right snap together before putting it on the window, once they're on the window and fully installed it's extremely sturdy. Again I wanted this to be a safe product.

What version 1 AND 2 comes with:
1.) No-see-um screen installed.
2.) Each side comes with an extra tab in the case of a failure. More can be purchased very cheaply, but I haven't had a failure yet with mine. I just wanted to include them for peace of mind.

Version 2:

After many requests and great feedback. I'm proud to present version 2 of my vents. These are likely the last iteration of this for quite a while as I feel I learned a lot in a short period of time, but feedback is always appreciated! The main differences between V1 and V2 are as follows:

1.) There's roughly 25% more vent area than the V1, while still keeping the plastic sturdy and the rain out.
2.) These are now modular, they allow attachments like a coming fan option or the coming "wedge" option. The wedges allow the window covers to be installed while keeping the front airflow possible.
3.) The new three piece design allows more accurate and better looking "inserts" that go into the window guides for securing.
4.) The slots for the windows are now tapered on both ends to reduce risk of damaging the window tint.

Which version is for you? I'm keeping V1 because I can keep it cheaper than V2 due to the less labor involved. It also allows some more peace of mind since it's a more solid piece of plastic. If you just want some ventilation and care more about safety then V1 is for you. If you want a modular (attachments) and more free flowing vent then V2 is for you. Both are safe, but V1 is going to hold up better than the window in most cases.