A lot of PMU and Tattoo artists use a pen-style tattoo machine today and needle cartridges should have membranes when used with these machines to prevent backflow into the machines and cross-contamination.
A cartridge may look like it has a membrane but there are a couple of tests to be sure! The easiest test is to use water or ink to test the membrane for leakage. (see video). The other way is to actually blow on the back end of a needle cartridge. If you hear air, there can be a possibility of backflow into your machine. DONT USE TEST NEEDLES ON CLIENTS!
Why would manufacturers even make needles without a cartridge? Keep in mind that some tattoo machines have a separate grip from the motor. So, in that case, you could use any needle as it's not leaking back into the machine..... if it leaks, it's only into the disposable or autoclavable grip.
This chart helps you pay attention to your hand speed, machine speed, and hand movements when using liners for a liner effect and shaders for a shaded effect.
It also shows how you can use:
A great go-to chart is just the beginning!