I agree with Martin (Milairjunkie) that the auto-on-off without a tank can be distracting. But I still prefer a twin piston over a single with tank. The twin piston runs cooler and quieter, thus, probably last longer. Even with a tank, the compressor motor still kicks on and off, but less frequent. Because it does not synchronize with my trigger action, it is even more distracting. I can live with either.
I started out with a twin piston compressor without a tank. It worked perfectly. But just out of curiosity, I added an airtank myself. It makes no difference to the compressor performance. But the auto-on-off is different as mentioned above. If the compressor is quiet enough to begin with, it really does not matter.
Martin has a business selling airbrush equipments. He is very knowledgeable about compressors. He may have a very good point about the low pressure setting problem. But I have not experienced that.
I love this forum which provides a wealth of information from a lot of knowledgeable users.