I do them with 2 companies and I tend to do it in work's time. I earned about �40 in 7 years, not much but every little helps.
Which companies are you considering?
It can be a little annoying when they ask you a load of questions then tell you you are not psrt of their target group. Mostly they ask you one or two to see if you are.
They do not need to be time consuming as you can choose if you want to take them or not. They usually say in the invitations how long they expect they should take.
I'd say between 10 to 20 minutges for each one. Some can be monotonous asking the same question over again. Sometimes I get product samples which is always nice. New juices and dog treats etc.
If "Axa Insurance" was a person would you say they were boring, vivacious, lively, old fashioned. If you can answer this codswallop then you'll be fine.