I looked at Viewer, and I find the method of having to move the slider to select the starting point to be annoying; I'd rather click on the note.
However, I then tried F5 on the Composer, and discovered that F5 means play from the cursor when stopped, and stop while playing. I.e. Click at start of phrase. F5 to start at phrase, F5 to stop, F5 start at phrase again.
So while it cannot play a phrase repeatedly, it'll make do for a singer. A little more anoying for an instrument player wanting to try the same over and over again.
I use Composer for rehearsing my choir parts, because I can alter the volume of the different parts, which Noteworthy Player cannot.
However, I miss the option to repeat a certain part over and over.
I'm disappointed even Noteworthy Player (I guess that's another name for Noteworthy Composer Viewer) cannot do a repeat of a section.
My optimal rehersal player would be where I can ealily alter the volume and instrument of the different parts, alter the speed, set a repeat from A to B, and see the notes highlighted on the sheet music.