Amp switcher

I have one and it works quite well. I have an Onkyo 875 receiver and a Cayin A88T tube amp connected to it. The switching is automatic upon powering up the Onkyo. No degradation in sound whatsoever. I use the Cayin for 2 channel listening and the Onkyo for home theater. Solved my problem of sharing the mains between the two amps.

Yes, any device you insert in the signal line will degrade the sound. The degree of degradation and your tolerance for it is unpredictable.

If switched accidentally while the tube amp may have even a little high voltage stored up may blow the output transformers.A poor connection in the switch may do the same.