I have done a Mexican grocery store chain for two different companies. I liked both of them. One had a generous reimbursement ($80 I think???) The other had a huge bonus, which was fine with me too. Neither of the chains have locations where I live, so I only do them when I am traveling.
A good portion of the employees at the Mexican grocery stores did not speak English. They had a look of dread and went to find a co-worker when I approached the counter. Surprise. I speak Spanish like a native speaker. Don't let the blue eyes and skin tone fool you.
I do a traditional grocery shop 1-3 times a week with a bonus. I quit doing any non-bonused ones, since I don't want to go more than 3 times a week anyway. These are super easy. I have something like 30 containers of Tide now. I have a preppers stockpile of everything at this point.
The really upscale ones that Johnb974 talks about, I don't do. He's not lying that they are a pain. They are good for free wine and cheese while you shop though. I find that shop odd, since nobody that works there can afford to shop there. You'd have to be making $200K and up to buy everything these and not notice the prices.
The other major grocery store chain had shops where you had to shop every department. Ridiculous. Those took an hour. I have not seen them in months though. Even with a $20 bonus and being on my way every day, I skipped those.