alternatives exist

RouterOS itself is a fine product, but it's a commercial product. You get a basic license with the board and it's good enough for a simple access point and it's also surprisingly easy to lose your license by reflashing the device.

I have several RBs running regular vanilla Debian for MIPS and I've had no problems at all with it. Recovering from a bad installation is also easy, the board's bootloader has built-in netboot support and is accessible through UART, so you just need to set up a DHCP+TFTP to serve recovery image and select it during the boot.

It's pretty much the best router-type device I've ever worked with. Head and shoulders ahead of ARM-based crapware home routers.