Question about the value of Output voltage ripple mentioned in power modules datasheets
There are two possibilities as expressed in the datasheet.

1) The ripple is highly dependent on output operating current. So if you are not truly
sourcing a very high output current (>= say 3A), your ripple will go down dramatically for
low power applications (e.g. 20mvpp for ~150mA, p5. fig 2.)

2) Additional input output ceramic capacitors of 1-4.7uF are expected to reduce (high freq) ripple between 10-30%. (Fig 19.).

If I had the part, I would experiment more in lab, as that number seems more like a max on the datasheet (they only show one value, rather than min/max range), when looking over some of the common operating characteristics.

Also, if ripple was a major concern, I'd probably try to first look around non switching based regulators.