Since we are an open-source project, let me explain a few things. In the previous mini PCIe pack (addon) for Turris MOX, we were selling Compex WLE900VX. This card is these days very hard to get. We can not wait until it is available. On top, some of you know that this card was and still could be problematic on Turris Omnia. There might be an HW issue/SW issue, and choosing between alternative firmware, which suits you better, can be time-consuming and not provide a good user experience. All these details were already discussed here on the forum.
We were testing multiple Wi-Fi cards, which we can use instead of Compex WLE900VX, so we would not stop the production of new units. We end up with card which uses mt76 driver. This driver should be more stable, and also it provides more features. Of course, I should not forget about higher Wi-Fi bandwidth, which this chip is capable of.
Since the previous card was 3x3, this one is 4x4. In the packaging, you can find only three antennas, and it does not matter how did you plug them since we continue to use it only as 3x3. If you would like to have four antennas, you are free to do it. These internal antennas are mostly for Turris MOX. If you want to use it on Turris Omnia, you don’t need to drill anything if you are not using an LTE modem or planning to get an AX card. There are already 5 holes (3 occupied already) in Turris Omnia, and you will most likely need additional antennas/diplexers (same applies for Turris 1.x).
In the future, as I said somewhere else, we are planning to provide and sell a Wi-Fi upgrade pack with AX (Wi-Fi 6) as we did it a long time ago for blue Turris 1.x with AC. We will announce it, don’t worry.
I don’t see why this card should not work for Turris 1.x routers. I’m currently using not officially supported by us - Mediatek MT7612E, which I was using with Turris OS 5.x and now with Turris OS 6.0. Anyway, If you would like to use this new card from this pack with Turris 1.x routers, you need to move spacers.
It will be added shortly to our FAQ.
TL;DR: This is a replacement for the out-of-stock Compex WLE900VX, and if you are planning to get AX (Wi-Fi 6) card, you should wait a little bit. 
This was only for users who bought Turris MOX: Start or any other variant without Wi-Fi and then they decided to buy addons with Wi-Fi.