A press release by the SatRevolution consortium says that it plans to send cubesats "as small as 50 kg" to Mars to "conduct a variety of valuable science." So that means orbiting, not just a flyby like MarCO-A and MarCO-B on 2018 Nov 26.
50 kg is a twentieth the mass of previous Mars orbiters. How could something this lightweight attain Mars orbit? The required delta V is about 3 km/s (there's no Oberth effect shortcut for an electric thruster).
At 0.058 km/s per kg, a Mars orbiter would need 3 / 0.058 = 51 kg of fuel, more than the mass of the entire proposed spacecraft.
Have thrusters improved so much since those launches that a 50 kg all-up weight is plausible?
Related buzzword (not yet a tag): tankage fraction.
18-page analysis of this kind of propulsion for orbit transfers: http://www.umich.edu/~peplweb/pdf/AIAA-96-2973.pdf