The Balisong or Butterfly Knife, despite its popularity is in fact illegal in many countries or States. The reason why it is illegal though is perhaps not because of its use as a weapon for committing crimes as much as for the number of people that get injured just practicing in their use. Before they became illegal, many people would practice tricks with them and in doing so would sustain cuts, often serious deep cuts which needed professional medical attention and it was that which caused them to become illegal. Today though there are what are known as training Balisong and these are very similar to real ones except the blade is not as dangerous and so cannot cause cuts of any kind let alone serious ones. Most real Balisong are expensive perhaps costing upwards of $200 but the training Balisong can be reasonably cheap, perhaps no more than $10 or even less. As they are illegal in so many places, the real Balisong knives are not sold on places like Amazon and so if you see one there which looks like a bargain, it will probably be no more than a trainer. You can learn more about specific Balisong knives here http://thebladeguru.com/our-best-balisong-butterfly-knives/but basically, as with most things today that are manufactured by more than one company, a relatively inexpensive knife can be very good whilst one of the more expensive knives is not so good and so if you want to buy one and live somewhere where it is legal to own one, you should still care in which one you buy.
The origin of the Balisong knife is often a point of controversy as some believe it to have originated in Europe whilst others believe it originated in the Philippines but certainly the Balisong is most associated with the Philippines. The word Balisong is thought to have derived from the Philippines region of Balisung where even today many of the knives are still made. The difference of opinion on their origin relates to the Philippine hero Jose Rizal, during a visit to Spain, introduced it to Europe or if he met it there and brought it back to the Philippines. Its popularity in the United States though was due to many American soldiers that served in the Philippines during WW11 brought one of these knives back with them. Their popularity in the US grew so rapidly that they were quickly being manufactured there but, this is what led to them being included in the ban in theSwitchblade Act in 1958 making them illegal. Evidence to support the theory that the Balisong originated in Europe can be seen at the Musee de la Coutellarie where a knife named the “Pied Du-Roy” is on display and which is thought to date back to somewhere between 1500 and 1700. So it would seem that even if the knife did originate in Europe, its name and its popularity can firmly be claimed by the Philippines and them introducing its use into their system of martial arts.