Hi,
I've done six of them so far. IMO, they are pretty good for additional practice – especially in verbal. The difficulty of verbal questions is said to be realistic enough. Also, their ‘feeling’ is true to the real GMAT, and in that they are much better than the verbal questions of alternative CAT-providers, even the best ones.
Quant is too easy there (esp. if you are targeting 45+), but also could be useful to train your stamina and to avoid careless mistakes.
Test structure for paper tests is different from the present-day GMAT, as you probably know; but still, they could give you rather accurate estimation of your score.
Overall, I think these tests are definitely worth buying if you seek to improve verbal.
For quant, I’d recommend Gmatclub’s Challenges.
Good luck!