Idea for this kind of spearguns is from В.Н. Крупяк 1970-80.
Gun design was patented by Борис Михайлович Клименко 1991. as Amatika:
http://www.amatika.com/
However Вланик (Vlanik) made real good working speargun from the idea of Крупяк.
His guns (Vlanik) are used by a lot of hunters without any complains.
Gun on the video above is made by С. Пономаренко using Vlanik gun design as a blueprint.
Also is used a lot and is reliable.
This is what I concluded from Russian forum. Credit goes to Vlanik for success of this design of speargun without piston!