Where Tanzania stands
Tanzania has not joined the Hague Apostille Convention, so an apostille for Tanzania does not finish a paper used there. Embassy or consular legalisation applies: the FCDO Legalisation Office certifies the document, then a consular stamp is added after it. Those are two different desks with two different jobs, and the register office copy that often precedes them is a third.
Three acts, not one application
People arrive expecting to apply once and be told where their case has got to. That is not how this corridor is built. Each office receives a sheet, does one thing to it, and sends it back. There is no shared queue, no joint file and no stage where somebody can see the route end to end on your behalf.
Nobody is holding the whole job
The practical effect is that the gaps between the stages belong to you. A sheet sitting on a kitchen table between two envelopes is not being processed by anyone, and no clock is running on it. Weeks disappear there far more often than they disappear inside an office, and nothing but your own attention closes that gap.
It also means a mistake found late is cheap to fix in one sense and expensive in another. The desk that spots it simply returns the paper; it does not correct it or pass it on. So the value of getting the first sheet right is not politeness towards the offices, it is the difference between one round trip and three.
Paying each desk on its own terms
The British stage prints its price: £45 / document by post, and £40 / document on the next-day line open to registered businesses. The register office charges for its copies, and the consular desk charges for its stamp, on a scale set well away from here. Three bills, arriving at three moments, is a more honest picture of this route than any single figure.