I agree. It doesn't look like a lifting handle, which you would expect to be centred, and where's the matching one at the back? It also looks as if it might be attached only to the top plate, so could it even take the weight?
It is a guard rail to protect the more fragile preamp tubes. It has been done since at least the 1950s.
Those tubes didn't give better linearity than "consumer" grade ones. Many of the best measuring tubes I've tested over the years were from standard suppliers like JJ or Electroharmonix.
The whole NOS thing is a rationalization of baseball card collector mentality.
When
I was in the guitar amp business from 2000 - 2010, I became quite a NOS tube collector. I recently sold that collection for over $15,000, which was a ~500% profit. The mystique around NOS tubes and tube rolling is alive and well.
You should see the current price of new tubes, though!
I learned that JAN tubes tend to have reliably lower noise and microphonics. Otherwise, most tubes sound pretty much the same, although they have different distortion profiles (the much debated "hardness" measure) from tube to tube, model to model, and brand to brand.
At the time, I purchased power and preamp tubes by the case from New Sensor and another vendor I cannot recall at the moment. Among preamp tubes, I failed roughly 40% for noise and/or microphonics being too high. Quality control was terrible. New Sensor would not accept returns, as they claimed guitar amps are too harsh an environment for their products, and they are meant for home hi-fi, which was an obvious disingenuous dodge.
Among preamp tubes, I found the Sovtek 12AX7WA and WB had the best quality control, but customers wanted EH at a minimum, found JJ to be acceptable, and really wanted T-S. Some customers would actually get angry if I shipped them Sovtek tubes. So, I threw hundreds of tubes in the trash. Sure wish I still had those to sell to Hi-Fi tube rollers about now!