Is the Vision M01 cage a good size for a parrotlet?

Technically yes, realistically no. Technically because the bird is able to flap their wings freely inside the cage. Realistically no, because any flying animal should be given a lot of room and better ability to exercise. I'd look at flight cages. They tend to be inexpensive compared to fancier cages of similar size and usually are roughly 4 feet wide, 1 1/2-2 feet deep and 3 feet high. Still small for an animal that can fly but at least it can make short hops etc...