While I mainly use Mikrotik router as LTE devices, I do have one site with an inherited Cudy LT something. Amazon is wrong, it’s not RouterOS. It has decent web UI, but all the features are pretty fixed in how they work and there aren’t a lot of customizations. Small example, Cudy’s do support ZeroTier but they don’t let you customize anything about it which then makes it hard to more granular route selection. Now, RouterOS offers way more flexibility, at the expense of complexity.
My point about “dual SIM” does not tell the whole story, while the number of modems does… basically a product that offers “dual sim” does not mean it run both at same time, unless it had two modems.
Personally, two LTE sticks to an RB5009/hAPax3/hAPac2/etc is an entirely reasonable approach. Mikrotik’s modems are pretty dated, and using LTE USB modems known to work in your country/carrier has some advantages over the generic modems Mikrotik uses since presumable they were tested by the local carrier. And since RouterOS uses the Microsoft’s MBIM modem protocol, most recent USB modem support. As noted, RouterOS should look for all modems on the USB bus, even through a hub. And RouterOS will act exactly the same in configuration as if it was a LTE-enabled RouterBoard, or just a router with USB modem attached.