Hi, I work for both of these companies, the pay is pretty good with Assosia, I do a long standing job with them. For Frontier, they have quite a lot of work available and the tax is already taken off what you earn. A lot of the jobs pay about £8 per job so fine. I have also found both companies friendly, woudl recommend them.
I joined Assosia about 9 weeks ago, in that time i have had 2 emails for jobs, both gone to faster fingers than mine LOL.. Pay does look decent for the tasks, but, they dont have a central database of tasks, you get what is emailed to you.
Edit: Have never heard of Frontier, a google brings up nothing that looks like a mystery shop firm... anyone have a link?
I have heard of them. There is a mystery shopping Facebook group, Mystery Shoppers UK Forum, https://m.facebook.com/profile.php?id=489715297793564 if you ask questions about specific companies they can help.