It certainly is fast - all file and folder names are held in memory, so it produces results as you type.
Fortunately for me, that's what I need most of the time as I file documents, pictures, TV programmes, films etc in folders whose name I sometimes forget. This search utility just couldn't be quicker without reading my mind.
There's no way the contents could be held in memory of course, so that is where indexing comes in. I don't know which utility is the best indexer.
For searching PDF files, I use PDF-XChange Viewer - it can search all PDFs in a folder and it presents every occurrence of the search item in a side-bar. But it is very slow because it has to read the files from disk.