Additional tests are inevitable as the proportion of Astars awarded means the pool of people applying for courses deemed desirable, but with finite spaces, is large and difficult to differentiate and why these MN boards are fully of threads (understandably) debating super-curriculars, PSs, courses with better applicant:place ratios etc.
My DCs exposure to additional tests has been via the TMUA (which has recently transferred to Pearson). Sitting it in October of Y13 and receiving receiving results (by paper and overall) in November helped them see where they were pitched nationally before deciding on their UCAS uni and course selection. This was very helpful and gave practical insight.
They signed up to one of the online AMSP courses (for state students) which was very low cost (bursaries also available) and comprised 6 one hour group sessions focused mostly on problem solving. So they got some support about how to approach logic questions but it was not OTT and did not require lots of free time etc.
Under the old TMUA regime, you could choose to release your results (or otherwise) to unis making reduced offers on the basis of good scores; this encouraged a 'have a go as nothing to lose' attitude. I am not sure that aspect has been retained under Pearson. However, additional tests, offering feedback by paper and, ideally, limited opportunity for the well resourced to dominate, can be helpful I would say.