The churches of Christ, in general, sing a cappela in worship. The reason is NOT that we think musical instruments are "of the devil". The reason is that the original church (in the New Testament) sang a cappela.
If you want a compaison, consider the communion loaf. You don't put peanut butter on it, do you? Why not? Is peanut butter "of the devil". No, it is not. Peanut butter is fine in its place - but it would tend to turn holy communion into a mere sandwich.
When the church sings together, we are all worshipping together. Adding instruments would perhaps make for a better performance, but a better performance isn't necessarily better worship. Not everyone can play an instrument, but everyone who can talk can sing (even if they are only "making a joyful noise").