How can I check if an ISA provider is legitimate?

[changefromhr]

Seen a niche ISA product. How do I check the company is legitimate? They are listed on FCA website but should I check elsewhere too?

Do you want to name them? Other users may have had dealings with them.

Red rose assurance/red rose friendly society

From what I can see online they would appear to be legitimate. They are a full member of the Association of Financial Mutuals, which gives me confidence.

That is not to say whether or not their products are any good, but that's a different matter.