Wow - tubemonger contacted me right away after this post and asked if I had any problems with their product. I have to say that's an impressive show of customer attention with their product.
However, I have never used any tubemonger product and my comment was just made as a general point of principle. In using socket-savers, you are introducing both more connective surfaces in the circuit and greater distance between the tubes and the rest of the supporting components. More connective surfaces mean an increased risk of connection failure over time. Greater distance can affect some high-performance tubes that are on the edge of stability in the first place. In some cases, I've seen SMD parts installed directly under the tube sockets because greater distances would lead to oscillation (6C45P, for instance).
Of course, the downside is that if you wear out a primary tube socket in your amp, it needs to be replaced. Coming from the DIY-side of things, I don't see that as a problem, but I can understand others would view it differently.
Anyway - as I said, all of that is a general comment of principle regarding tube sockets in general. It has nothing to do with tubemonger's products specifically.