I started contracting with Big Fish in Sep 2021 after over 14 years working through my own company (outside IR354).
The number of Umbrella companies out there is staggering and I checked several of them and also talked to independent umbrella company advisors in order to make a choice.
Big Fish cam up tops in all the reviews I looked at and since joining them I haver had no cause for complaint. They are efficient, timely and approachable. I've only had a couple of minor issues during the last 6 months and these were all dealt with and resolved promptly.
From what I can see with other larger global, especially "offshore" umbrella companies Big Fish is top of the list. You are able to contact them by phone, they pick up and their staff are polite and helpful.