It's very good preparation. I've been using it for some time in anticipation that we would have the chance to move to the U.K.
Good to get some practice, though do be aware that although the test can be taken at any time after you have moved to the UK, you have 5 years' worth of spousal visas to get through first before you actually need to pass the test.
The test is only required for ILR (permanent residence), followed by UK citizenship, and it takes 5 years of living in the UK to qualify for ILR.
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