Firstly, is it legit? Yes.
I have personally made hundreds of pounds from the site.
How does it work?
It is a user testing site, where researchers are able to recruit participants to test products, ideas or get feedback on something.
It is one of the highest paid research sites around. They use online software for you to fill out a survey and make money quick online. It's an easy way to make money online in the UK.
If you're picked all you need to do is follow the instructions on the project. They tend to be pretty straight forward. But, often with respondent.io they require industry professionals for the project. But there are so many projects you likely will qualify for something.
Just make sure you're honest on the application, you must be to talk about what you've said otherwise you probably won't get paid.
What will I do?
You apply to projects by completing 'screeners' if a researcher thinks you're a good fit then they will add you to the session. You confirm the data and time, attend and then afterwards you're paid. Easy.
Should I verify my work email?
Yes. verifying your work email address is one of the easiest ways to increase the likelihood of getting accepted for studies. You receive a link to your work email and you just need to click on it. Also, if you connect your LinkedIn then researchers are able to tell you actually work in the field you claim.
I have found this makes a huge difference to the number of projects I am accepted on.
How much can you earn?
This will depend on which projects you get accepted on. If it's difficult to recruit for, for example if it's a highly specialised skill they need then the recruiters will pay more. (see below). Without too much effort I've got accepted on to a quite a few projects all paying between $50 -$100 dollars an hour. So it's a great, easy way to earn money online.
How do you get paid?
Respondent will pay out via PayPal once your attendance has been confirmed (proof below). Normally this is a few days after the study but it can take up to 10 days. Also, Respondent take a 5% fee themselves.
You'll get the USD in your PayPal account then you can withdraw to your bank account.
Summary
Overall it's a great site to sign up and start doing projects. You can earn several hundred dollars an hour all from working online from home.