I have one mini mill. It's about 2 1/2 years old.
I do some steel (4130,4140,) and some stainless (15-5,17-4).
But I don't mill anything with heavy cuts. I use small depths and fast feeds. I do this on all my machines, big and little. I feel it's better all around. Better for the cutters, better for the machines, and mostly it's faster. JMO
I have been very happy with the mini mill, and all my Haas's.
You just have to remember your not buying a VF6. There isn't much mass to absorb all the forces.
I have one Haas (VF1) that is 13 years old and all we do on it is one part, 1117 material, and it still is going strong. That's all it ever been used for that one steel part. Still holds good tolerance and it runs almost every day, has for 13 years. Very little done to it at all. Man come to think about it, that machine has made us a lot of change over the years.