Not great
Paystream started off great, but they have a weird approach to expenses. If you spend over £40 on subsistence (which is entirely possible at an airport with current rates of price inflation), Paystream will only permit you £40 of expenses and the remainder of the expense is treated as income, meaning you pay tax. Paying tax on a business incurred expense is absurd!
Paystream say that they are administering the regulation set out by HMRC, but HMRC don't give any guidance on a limit. HMRC’s own words https://www.gov.uk/hmrc-internal-manuals/employment-income-manual/eim31837 “A simple list of agreed rates would run the risk of permitting excessive relief or being inadequate and so of little practical use.” Paystream picked a universal and arbitrary £40 limit out of thin air. Clearly they've never had to have dinner in an airport.
If you don't have expenses as part of your role (or they are always below £40) then Paystream aren't a bad umbrella. If you're incurring expenses for subsistence beyond £40 you'll be better off with a different umbrella (make sure you ask how they treat subsistence expenses).
The worst part of it all is that I only noticed that I was paying tax on my expenses once I reconciled my expenses against my payslips. Paystream didn’t proactively tell me that they were adjusting my expenses. I feel like they were hoping I didn’t notice.