First thing: they are in tune.
Second thing: they are loud. If you don't push them hard enough, they don't make any sound; and when you do push hard, it's loud.
The sound is very bright - as one would expect from bells - and they will give you a headache if your kids go crazy on them.
There lies the potential problem: as an instrument for grown ups to use, they will soon frustrate you. One octave, only a C major scale, you will want more (in range and chromatisms). As a toy for kids, again, they are loud.
But if you are ok with it, they do exactly what they are supposed to do.