At present, to call these "editors" is misleading, since one cannot actually edit anything in them. (If there is a way, it is not documented, and I haven't been able to find it by experimenting.)

I have an almost 20-year-old, almost-free MIDI sequencing program with a piano-roll editor that allows:
- Note entry, deletion, etc.
- Dragging to change duration (note-on and note-off)
- A second pane across the bottom of the window allows dragging to change velocity
A separate but similar editor allows dragging to change tempo. This is very useful for phrasing, and goes a long way toward making playback less mechanical sounding.

No, it's an ancient version of Cakewalk Express. I forget the version number; 3.0 maybe. For a $10 program, it has some fairly nice features for composing, but is very poor at printing. (Not too surprising, since it's designed to be a sequencer, not a printed notation program.) I'd still be using it, but my installation is damaged (playback produces no sound), and I can't find the CD to reinstall it.

I found MuseScore a few months ago when I was looking for a free equivalent, and I'm very happy with it. I just discovered musescore.org today, and I've found workarounds for most of the issues I've been having with it, and found shortcuts I never knew existed. :)

If you view MuseScore only as a notation program, perhaps not. However, if one uses MuseScore as a composition tool, and one wants to hear what one has written, it can reduce the effort of changes that would require laborious, note-by-note changes in the score.