I’ve been using it for a bit over 10 years and have earned $241.27 in Google Play credit for 946 surveys. The credit expires 1 year after being earned, so you can’t accumulate it indefinitely. I use it occasionally for a paid app, game, book, or movie rental.
I must have allowed access to location data for that app, as it asks questions about places I’ve been recently. It’s actually hit or miss with getting the right place, so I think they use it to improve accuracy with what store is being visited based on GPS. I’ll also have it ask questions about whether I made a purchase, how I paid, and if I have a receipt, if I’d scan it. I also get them about purchasing intent based on Google searches that I’ve done. And there have been several recently asking to compare search results, with an increasing focus on comparing a page with AI results vs. without.
The surveys are generally very quick. I actually get sort of excited for them because it provides a bit of playing around money to use for entertainment that I somehow have more aversion to spend if it’s coming from my bank account.