As noted in my last post the sources regarding these weapons are limited however I have tried to cover what there is. It should be noted that the term Morning Star is a mace that has spikes, not a type of flail - for some reason I have encountered this misconception a fair bit. The European material is really hardly relevant - perhaps the Roman net and trident may relate but when I began looking at that particular set it led nowhere useful.
Flail of Mair
According to Wiktenauer, Paulus Hector Mair (1517 – 1579) was a 16th century German aristocrat, civil servant, and fencer. He was born in 1517 to a wealthy and influential Augsburg patrician family. In his youth, he likely received training in fencing and grappling from the masters of Augsburg fencing guild, and early on developed a deep fascination with fencing treatises.
The flail shown in Mair is a two handed weapon. This sort of weapon can be seen in some medieval paintings and seems to have been used amongst other things for attacking those on horse. They were obviously developments of agricultural flails. Because of this its relevance for us is low and I have only shown a few frames. There is also sickle and scythe, but no hint of there being a chain attached…
von Baden Flail
Jakob Sutor von Baden was a 17th century German Freifechter. He seems to have been a native of the Baden region of southern Germany, and was an initiate of the tradition of Johannes Liechtenauer. In 1612, he authored a fencing manual which shows a clear relationship to the 1570 treatise of Joachim Meÿer and the 1611 treatise of Michael Hundt.
There is only one plate, again the Type is 4:
'When two fight with flails, it often happens that both staves become bound together in the middle; when this happens, stay on his flail staff with yours, and let go with your left hand; invert it, grab both staves, and go through below with the butt of your flail. Press upward toward you with your right hand, so he must let go, or fall when you step back with your right foot.'
Talhoffer
Talhoffer’s various works include a tiny bit of flail. This plate simply shows a design - he had many plates that were somewhat of a catalog of fanciful medieval equipment of all sorts.
General European Flails
Obviously the use of the flail as a weapon by the time people began compiling this information was limited - most likely it was very much limited in warfare much as with Japan. The flail in some form did exist as an agricultural implement which may be why it is covered at all - for judicial duals in some areas.
In terms of warfare there are examples of both the Type 2 & 4 present - we have seen in the treatises only examples of the Type 4.
I'll let wiki take it from here: The longer cylindrical-headed flail is a hand weapon derived from the agricultural tool of the same name, commonly used in threshing. It was primarily considered a peasant's weapon, and while not common, they were deployed in Germany and Central Europe in the later Late Middle Ages. The smaller, more spherical-headed flail appears to be even less common; it appears occasionally in artwork from the 15th century onward, but many historians have expressed doubts that it ever saw use as an actual military weapon…. A few doubt they existed at all due to the number of pieces sitting in museums that turned out to be forgeries, as well as the unrealistic way they are depicted in art. Archaeologically, however, a type of military flail known as a kisten, with a non-spiked head and a leather, rather than chain, connection to the haft is attested in the 10th century in the territories of the Rus, probably being adopted from the either the Avars or Khazars. This weapon had spread into central and eastern Europe in the 11th - 13th centuries and may be considered an ancestor of the ball-and-chain flail. Waldman (2005) documented several seemingly authentic examples of the ball-and-chain flail from private collections as well as several restored illustrations from German, French, and Czech sources. He states that the scarcity of artefacts and artistic depictions, combined with the almost complete lack of text references, suggests they were relatively rare weapons and never saw widespread use. One of the reasons was the hazard the weapon posed to its wielder, especially the varieties with long chains and short handles. A missed swing would still retain momentum, causing the striking end to continue its arc around, potentially into the user's hand or body.