If this person would like to ask in the interviews they might get a more personal recommendation.
It is not black and white. Some people are not really ready for a 20-day retreat. If you feel you are ready for it, I would say go for it.
If you are not really certain you are ready for it, then doing a 10-day retreat at Wat Kow Tahm, another one here, maybe this particular type again, that could be better.
So, it really depends on you and your abilities. We are happy with the results of both the 10 and 20 day old students retreats.. It is much tougher, due to its length and intensity.
In regards to reflection meditation, the 20 day retreat has some that are not taught in the 10 Special Old Students' retreat and vise versa. So, as far as the reflection side of the practice, you are getting a lot of it here, as much as people get in the 20-day. What the 20-day has as well is some pretty intensive Dhamma talks.
So, if you are ready for some more work, yeah the 20-day would be fine.