I would absolutely keep one in there, male or female.
In fact, in a discussion on the board not long ago, I said that Lucky lived in one JUST like that for months, and that's in fact where he grew his tail back. Six also lived in one for the same amount of time and they both were perfectly happy with life.
They each just had a little silk plant in there with a thin layer of gravel and they did fabulously in them.
They have both since been upgraded to 2.5G tanks, just because I could and I had the room, money, time, etc. BUT - if it came down to it, I would not have any reservations about keeping one in one of those for the long haul.
My feeling is that if a fish is kept in sparkly clean water with decent temps, gets fed a variety of foods, and has some attention paid to it each day, it will flourish, even in a container this size. Besides - it's not like they're being "downgraded" to a tank of any size - they're coming from a cup. Whatever they go into is an upgrade for them, and their quality of life, in my opinion, very largely depends on us as fishkeepers rather than the size of their tanks.
Of course, all just my opinions.
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