Looking furher at that SMACO web page (
SMACO S300 0.5L Plus Scuba Diving Air Tank) it's a blob of marketing BS. They are claiming "5-8 minutes" (although further down the same page it states 6-10 minutes) of time. I'm going to assume you are not familiar with diving and gas consumption, or for the benefit of anyone else who stumbles across this thread in the future via a search engine.
Gas is consumed at a rate referred to as the Surface Air Consumption (SAC) rate. It's how much air you consume, On a basic dive where I'm easily swimming around I'll run around a SAC rate of .5 to .6 CFM, which means I consume 5 to 6/10th's of a cubic foot of air per minute (CFM) at the surface (out of the water). For every 10 meters/33 feet you increase your atmospheric pressure by one, and your SAC rate is multiplied by the total atmospheres of pressure you are working at, or ATAs. So at 33 feet you are at 2 ATA, so in my case I'm consuming 1.2 CFM (.6 CFM x 2 ATA). That bottle (.5 liter @ 200 bar of pressure) holds 3.5 cubic feet of air. So going down all of 33 feet, I'd have less than 3 minutes of air from that S300 bottle. Freedivers can breath hold that and then some. And they don't need to get our of the water and go back to their car to use some some wonky compressor hooked to their car, or doing "600-800" pumps on a high pressure bike pump. Heck, at one pump per second that's 10 minutes, non-stop without a break.
Even going down to just 10 feet (1.3 ATA) it'd last me all of about 4 1/2 minutes. By comparison a standard scuba cylinder will give me over an hour and a half at that depth. Or for the 33 foot depth, over an hour.
Now then, most new divers will run a higher SAC. Also, the more active you are, the more you are breathing, the higher your SAC. My SAC rate will go higher the more active I am. If you are more active, having to swim and keep yourself down, I can easily see a SAC rate of 1 or higher. So, you get a whole minute and 45 seconds at 33 feet, or 2 minutes and 40 seconds at 10 feet. And it only gets worse the higher the SAC rate.
So you manage to get down to 30 feet or so to see the pretty fishes. Only you quickly lose tract of time and go to inhale and only get a partial breath as the tank empties on you. So you quickly race to the surface only to find yourself couging up blood as a result of a lung over-expansion injury since you haven't been properly trained on breathing compressed gas at depth. If you're lucky you've got lifeguards on the beach and an ambulance nearby to get you to the hospital in time. In a semi-remote location, well, there's a reason I refer to those as suicide bottles.