CHIKADIVC300 Mini Scuba Tank Refillable Oxygen Cylinder with 0.5 L Capacity Scuba Tank with 5-10 Minutes Underwater Diving Gear for Diver Portable Diving and Snorkeling

Firstly, Extracting pure ‘Oxygen’ from air is an expensive process which is not achieved with a hand pump!Secondly, Scuba divers do not use 'Oxygen' cylinders except in cases of emergency at the surface. Instead, they use 'Compressed Air.' This is ordinary air found above ground level anywhere in the world which is then compressed (with the use of an expensive 'Compressor') into the diving cylinder at great pressure. In simplistic terms, that compressed air is then eked out little at a time, to the diver throughout the length of the dive.Leaving aside all other issues I will explain the maths. The air we breathe is made up of 21% Oxygen which, when breathed at depths of over 85 metres (approx 275 feet) turns toxic (i.e. poisonous!) and will kill. BUT!, if those same diving cylinders were filled with 100% Oxygen it turns toxic at depths of just 10 metres (33 feet!) as any competent diving instructor will explain.One customer has asked if this is all the equipment his children need for scuba diving in their swimming pool. I wonder if he’s now checking the depth!!!If the manufacturers of this questionable item of equipment do not understand the basics of oxygen, air, depth and scuba diving in their most rudimentary forms they should NOT be making such equipment. Avoid all contact with this device. It is clearly not fit for purpose and certainly not fit for the minimum one star rating I am required to give.NM(Active diver/instructor for 45 years)