Cleartune 4+

Like all apps of this type it is distracted by background noise and useless if other instruments are being tuned at the same time. So don't use it if you're in a band onstage.
Otherwise it's pleasant to use, although a bit expensive compared to others. I just tuned my six string acoustic with it and it worked although the needle did fly around a lot once it showed the note.
I've tuned my flute with it and it was useful and the needle held against the note afterwards. I found it useful in getting the pitch right for other flute notes.
With an electric guitar you would have to plug it into an amp as well, probably, to get the volume but I haven't tried that yet as that equipt is packed away.
Ultimately you're limited by the device itself -ipad, iphone etc.
Take it for what it is, something you'd use in the house or other quiet area.

My banjo tutor has this app, and as my old stand-alone chromatic tuner is not working as well as it should, I decided to purchase it.
This is where the One star comes in, the developers don't inform you, that if you have an iPad mini 4, that although it downloads, it won't work! Seems as though the app can't hear the notes, might have to take it to Spec-savers hearing centre for a checkup.
Luckily though, I have a small orchard of gizmos, including an iPhone and an old iPad2 and via iTunes, down-loaded the app to them, and it worked first time. But, I didn't really want to use either of those apples as they both have small memory banks.
So in conclusion, if you have an iPad mini4, DON'T purchase this app, today it won't work, and the developers don't seem to give a ........
The Four stars? Well, if you have a gizmo it will work on, e.g. The larger iPads or iPhone then it has some great options, unfortunately most of them go over my head as, there doesn't seem to be a manual or operating document for it.

It's a great relief that Cleartune lives on. I thought I would lose it on upgrading to ios 11 and there aren't many good alternatives. I use it to give notes to singers, and it is easy to use but flexible. There are many settings for pitch, transposition and temperament and you can create presets of any of these. UPDATE - Minor problem: you can't delete presets as the app crashes if you try.

I would prefer to see five notes on the pitch pipe dial like before, not just three.

It can of course also be used to tune instruments.