They are better than using just inhaled oxygen. The pressure helps to push the oxygen further into the tissues, getting more benefit. Interestingly, there was a study at the VA hospital in New Orleans where they used h-bot chambers with and without oxygen, and they found that the patients in the pressurized chambers without added oxygen improved from baseline, so they had to discontinue and rethink their study. The message was that the pressure helps, and that the oxygen has an additional beneficial effect.
You can increase the partial pressure of oxygen in two ways: (1) by increasing the oxygen concentration in the the air, and (2) by increasing the overall pressure of the air inside a hyperbaric chamber.
So even if you breathe normal air inside a HBOT chamber, you are increasing the partial pressure of oxygen.
And if you breathe higher than normal concentrations of oxygen (eg 100% oxygen) at normal atmospheric pressure, outside of any chamber, you are also increasing the partial pressure of oxygen.
The higher the partial pressure of oxygen, the more oxygen is dissolved in the water of the blood.
So even a HBOT chamber in which people breathe ordinary air is going to have a higher partial pressure of oxygen.
It's possible increased ambient pressure might have some health effects unrelated to oxygen, and maybe that's why soft HBOT chambers have benefits.