A Completionist is getting 9 free ranks on each of the 20 virtues, 180 in total. 34 deeds to max a virtue instead of 43 deeds under the new system. That 180 is just over a quarter of the virtue deeds they have already done. Not to be sniffed at.
It's better if you are a bit of a slacker completionist then you get the bonuses and enough left over to tweak things with a few more completions under U24.