I can't tell you about the RigExpert ones, but I own a MiniVNA tiny and I love it.
It has its drawbacks of course, but it's still surprisingly competent as a VNA. I used it to measure some UMTS and LTE antennas and, compared to an Agilent E5061B, it held its own quite well. Of course it's not the same thing, but it's not a toy either.
Looking at the RigExpert, both are VNAs. RigExpert doesn´t give a dynamic range figure for their analyzers, although I guess it will be in the same order of mafgnitude as the MiniVNA.
I think the main difference between them is the intended usage. The MiniVNA tiny is a rather complete VNA offering S11 and S21 measurements (which means, you can measure filter bandpass with it) and the RigExpert are more specialized antenna analyzers. The RigExpert is much more convenient to use in the field or on a roof, and it is more flexible regarding measurement impedance. The MiniVNA Tiny is fixed on 50 ohms.
So: to summarize. Considering lab usage beyond adjusting antennas? MiniVNA Tiny. Need something flexible to carry to the field, maybe to a rooftop, and you don't need S21 measurements? RigExpert.
Cheers,
EA2EKH