... The low frequency support is in the plans and I'm starting to prototype various ways to do it. I think the main competitors will be the lower end of the professional offerings (copper mountain, picotech, etc) rather than NanoVNA related products. There are actually some aspect where we may be able to beat the professional offerings, like temperature drift and low frequency performance. But with the budget constraints things like sine wave output and wide adjustable power output probably won't make it.
I don't see you competing with the professional products but instead forging a new niche area.
All of these profession units will be sine wave drive. Some support log sweep, bias Ts, adjustable level. Freq range, tempco, noise, dynamic range for a few low cost (<$25,000 USD) portable units:
Pico Technology PicoVNA 106
0.3 MHz to 6 GHz at 10 Hz resolution
± 0.005 dB RMS ± 0.02 dB/°C. Measured at maximum bandwidth.
Transmission: ±0.1 dB, ±1°
Reflection: ±0.5 dB, ±4°
Dynamic Range: Typically: 118 dB @10 Hz
Guaranteed: 108 dB 10–4000 MHz 100 dB 0.3–6000 MHz
Copper Mountain S5065
0.01 MHz to 6.5 GHz at 1 Hz resolution
± 0.0021 dB RMS ± 0.02 dB/°C. Measured in 3 kHz bandwidth.
Transmission: ±0.1 dB, ±1°
Reflection: ±0.4 dB, ±3°
Dynamic Range: Typically: 130 dB @1 Hz
Guaranteed: 125 dB 0.3–4800 MHz 120 dB 0.3–6500 MHz 75 dB 0.1–6500 MHz
Tektronix TTR506A
0.1 MHz to 6 GHz at 1 Hz resolution
± 0.008 dB RMS ± 0.015 dB/°C. Measured at maximum bandwidth.
Transmission: ±0.2 dB, ±2°
Reflection: ±No spec. dB, ±°
Dynamic Range: Typically: 122 dB @No spec. Hz
Guaranteed: ≥124 dB typ. 2–200 MHz ≥125 dB 200 MHz–3 GHz ≥122 dB 3–6 GHz
Anritsu Shockline MS46322A-008
0.05 MHz to 8 GHz at 1 Hz resolution
± 0.006 dB RMS ± 0.02 dB/°C. Measured at maximum bandwidth.
Transmission: ±0.08 dB, ±0.5°
Reflection: ±0.37 dB, ±2.2°
Dynamic Range: Typically: 115 dB @10 Hz
Guaranteed: ≥100 dB 10 MHz–8 GHz