I can't use TextPlus with FitalyLetris
as the aim of FitalyLetris is to develop the writing speed itself I never tested to use it with TextPlus. Also any word or sentence completion is excluded from the contest, because otherwise a user of Fitaly for PocketPC could write it within 2 seconds, and that is not what we are looking for :-)
So it is good that you tested and found out.
Nevertheless word completion can be practical - it is just another issue.
Technically, FitalyLetris expects letter per letter input and compares them one by one. So maybe TextPlus uses another method for entering text.