The 'routercnc_MK3' is my machine and I'll explain why it looks like that.

It was much easier to build it like that based on a simple evolution of the previous version. It is only intended to cut balsa wood, liteply, and plywood and it works very well. I've been using it recently for cutting some 20mm thick aluminium upgrade parts, but that is not the main use.

If I do cut aluminium on my machine (6mm carbide 2 flute cutter) I can run at 1.0mm depth of cut and about 800mm/min feed. Any deeper and I get chatter.

If you want to cut a fair amount of aluminium the raised X axis designs are far superior and probably the best DIY CNC arrangement without simply converting a bridgeport mill to CNC. If you are starting from scratch there is no reason not to really.