The individual who has carried out the testing on the Fezz in the Link, is with a decent reputation for their work done in audio related equipment.
https://www.diyaudio.com/community/threads/fezz-audio-titania-test-and-review.405479/
If Tube Amplification/ Tube Devices is a new encounter, there are disciplines worthwhile learning about and adopting when using Tube devices. There are many Tube users, inclusive of myself, that strongly suggest a different approach to using SS devices, is to be practiced when using Tube devices.
Tubes can become extremely hot (Red Tube) when a fault has manifested, which if not intercepted and Powered Off, can become a fire!!
The Link is showing a individuals experience, there are many experiences to be found, in this case the individual has had their eyes on the Tubes, and got lucky to to their intervention.
https://forum.audiogon.com/discussions/tube-fire-what-next?highlight=Tube%2BFire