Hi slegne
New Style ESA is a Contribution Based benefit and is not means tested with the exception of pension income which can reduce the amount that you receive.
The Income Related benefit that goes with NS ESA is Universal Credit.
NS ESA will end after 365 days unless you are in the Support Group at that time.
If your son is found fit for work after going through a MR and an Appeal then he will have to apply for Universal Credit.
Our UC and ESA claim guide explains the criteria that your son will need to meet, make sure you read page 27 and page 135
www.benefitsandwork.co.uk/help-for-claimants/esa1 If you have any further questions please come back to the forum.
Gary