I did it a cpl yrs ago, with 3 (4?) Cos.
It wasn't worth the time it took. Came out to about $5/hr.
Finding assignments (diff co's call them diff things), reading the details of them, driving, finding parking, photoing receipts, filling out the questionairs, tracking my time, mileage and the $$...
I'm a quick typer, so I thought I'd be more efficient.
Test driving new cars was kinda fun, though.
Only had 2 meals I actually enjoyed.