Avantages
Management generally leaves employees alone except during contract renewals. Your "real" supervisor is your government FTE (Full Time Employee) not ERT.
Inconvénients
After working as a contractor for 7 years I was eventually unceremoniously told that my contract was only going to be renewed for one year only and relocated to a place with a much higher cost of living (with no COLA). It was clear that ERT didn't care about the loss of my experience and knowledge that I gained over many years. This revelation was closely followed by the recent government shutdown where ERT made it abundantly clear they had no intention of helping contractors such as myself get reimbursed for lost PTO I was forced to burn during the 14 day shutdown (other ERT contractors were at least allowed to work part time). The failures of ERT essentially boil down to the uncertainty surrounding future contracts coupled with the lack of performance-based advancement metrics. It didn't matter how well you did your job; raises were solely dependent upon how much money was left over after ERT took their cut from the contract. Hiring freezes within the government likely did ERT no favors either.