The 22.4% sodium chlorite solution is dangerous to handle. The 5% solution is much safer to handle, and much easier to measure.
The effectiveness of these solutions are based upon the available and free chlorine dioxide in them not on the concentration of the raw material. You can do everything with 5% sodium chlorite that you can with 22.4% sodium chlorite and it is much safer to handle.
If you are backpacking and carrying everything you have on your back, there would be an advantage to the higher concentration solution because it would weigh a little less. However, even when backpacking I still carry 5%. The savings in weight are quickly offset by the complications involved in safety in the event of a spill or accident.
If you happen to read Jim Humble's book you will find that he also states that you can do everything with 5% sodium chlorite that you can with 28%.