On a technical point - a modern microlight is no less robust than a light aeroplane, and in the UK also you need microlight differences training (probably only an hour or two for an SEP rated pilot onto 3-axis microlights). But, there may be issues if he wants to fly in night/IMC with the aircraft.
Then again, there are probably far greater issues for anybody who wishes to fly at night/IMC into a small farmstrip anyhow, regardless of what they are flying.
The cost of doing differences training / rating for microlights is likely to be comfortably outweighed by the savings in running a modern microlight compared to something with a Lycoming and CofA.
G