The idea on certain designs of Valve Amp having as part of the design an ease of access to the Valves, resulting in a very simplistic requirement to exchange a Valve is very attractive.
As exchanging Valves can and in certain cases do create a difference to an end sound that is discernible for the impression made of being more attractive in use.
Then there is the alternative side and the one why many Valve Amp Design have the Valve visible to the user. That reason being easy observation of the Valves during use and after Power Off.
There are not many who have a long term understanding of using Valve equipment, that would suggest a Valve Equipment is something that is switched on and forgotten. The Valve equipment is at its very best, when the user is disciplined to be vigilant in their observation of the equipment when in use and after Power Off.