In my opinion full-text search is most useful to search for examples (usage), some phrases (including proverbs), etc.
(Looking for rare chars and terms also is very useful, but that's another story).
So it's OK if the search in Pinyin will require tone marks (or may be even no tones if more than one char/word in search?).
Pinyin has many good sides and most useful (at least for me as a beginner) - it's easy and quick for typing.
So in F-TS case it can be used just for quick typing and in this case tone requirement is OK (at least it's better than no Pinyin at all).
PS: and sometimes I don't know/cannot remember how to write some phrase, but do know how it sounds (i.e. can write pinyin with tones, though it's even better if I can search a complex phrase without tones).