The main issue is precision. Harbor Freight ones will not have the precision required to send a steady flow of bubbles...they are made for off and on use, not for the needs of precise metering of the gas. Choke it up and buy a good one. Harbor Freight is not the place to buy quality products because they don't sell them, they sell seconds, refurbs and import stuff no one else wants. Do you really want a tank of highly compressed gas being controlled by a valve that could let go and launch that tank across the room?