Eg. https://www.opengearstore.com/ProductDetails.asp?ProductCode... - PCIe UARTs rather than USB, 2 GbE ports, a bunch more software smarts, and support.
I wonder what that overkill in speed is for. With serial ports you don't need that much bandwidth (48 ports x 100 kBits = 4,8 MBit/s, yes I know it's 115200 but too drunk for math). You could even run that thing with a 10 MBit/s LAN interface.
The only thing I understand is the PCIe stuff because USB latency can be problematic (especially on the Pi).
The problem with them is that they use just an 8051 microcontroller (talking to an ethernet controller over a parallel port)! Arp and other broadcast background traffic on modern networks overwhelms them.