Space is limited on them...hence the name Mini-Mill. Also a minimill is lighter on power and torque...but it's a mini...take mini cuts and take 'em fast.
Does it have a 4th axis or is it wired for a 4th axis? Big difference as a rotary 4th is a chunk of change and if included machine is a steal. Wired for 4th is nice...never know when it will come in handy, just buy one and go. FYI- not all their 4ths are Plug and play, brushless or brushed may need new cables or a converter box to make work. Unless just running using an M-switch.
Haas makes 4th axis work so easy...layout as flat work, enter diameter in setting, lock the axis part revolves in relation to and with a quick g code the program wraps itself around the part. 4th is also nice to machine other sides of parts.
To your question, I have Haas machines going back to 91 still running 8-10 hrs, 5-6 days every week for years. While I do cut alum, brass and plastic, I also cut a good amount of steel, alloy steel and SS. Controls are solid, easy to use and yes Processor may go bad with high dollar Haas replacement...but they can also be rebuilt as an option. To date only one of my 8 Haas machines ever needed a processor replaced with years of time racked up on them.
Good luck.