One of these circuits appears to be a modulated power oscillator, meaning the operating frequency would likely change based on antenna loading changes, and with modulation...poor man's FM.
Yes and I'm going to expand on this a little:
Transmitter have several operating functions inside them. Examples are, an oscillator (a VFO is one such oscillator), a final amplifier and perhaps some amplification between the two of these, perhaps some sort of power supply (e.g., 'bias") circuit. All those functions have to be present and operate well separately from each other; this implies a level of isolation and is critical for proper operation. If the different functions interfere or interact with each other too much, bad things can happen like muddy/mushy modulation, FMing or frequency shifting with modulation, oscillator drift, feedback (instability), operation at unintended frequencies and so on.
The best way to ensure a certain amount of isolation is to make separate oscillator circuit, a separate final amplifier circuit, separate power supply circuit and then the designer will weave them together so that they all "play nicely" with each other.
The single tube/valve transmitter shown doesn't have any of that isolation between circuit functions; it does all the functions in one circuit and so it is prone all the issues I mentioned above. So why do it? Having those functions in separate circuits adds complexity, expense and time to build. For a hobbyist, convenience may override all those other considerations.
