(On this benchmark, MBps means one million bytes per second.) You very helpfully ran CrystalDiskMark when I asked, and it put the read speed at 16.28MBps and the write speed at 6.52MBps. If your 1TB Flash drive reliably holds 1TB for a year or two, then it’s unlikely to be fast.
As mentioned in the comments below, this is almost certainly a scam, because the old computer industry adage still applies: “cheap, fast, good – choose any two”. I was surprised – shocked! – to discover that you could buy a 1TB flash drive for less than a tenner, because I’ve been paying more than that for 16GB and 32GB versions. Could you use one of those as a normal day-to-day drive? I will use one as a backup, but if I mirror my drive on it, could I switch over to it if my drive goes down again? Roger I have just had to replace my 1TB hard drive, which cost £25 all done and dusted, but I notice you can now get a 1TB USB Flash drive for £8.99.