(This plant comes in a 3.5 inch pot. You will receive a very similar plant to the one in the picture. It may or may not be blooming at the time of your purchase. The plant is shipped in its pot to prevent any damage to the roots).
Rebutia krainziana has very nice red flowers. This plant flowers consistently and prolifically.
The "normal" and more frequently seen form has bright orange-red flowers, but color variations of ranges in shades from dark red, to orange, yellow to pure white.
Cultivation: Full sun to light shade. Water regularly in summer but do not over-water. Keep dry in winter. Hardy down to -4°C.
It is better that they be re potted regularly. Re potting will increase the number and size of stems, and will increase the number of flowers produced. Re pot yearly until it reaches about 100 mm in size, then every two or three years will suffice. Re potting is best done at the end of winter, but it can be done at other time, too. Do not water for a couple of weeks after re potting, in order to reduce risk of root rot via broken roots.
Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz