Personally I wouldn't entirely trust any company trying to sell themselves to you based on their previous students' Umat scores. Sure, good umat marks might also be indicative of good ucat marks, but these Australian companies are generally new to the whole system and really rely on profits from students. They'll do their best to market themselves as good prep companies but there's no evidence yet that their teaching method works.
Compare this to previously established UK companies which have their materials prepared for the ukcat, the same test that you'll be sitting. I wouldn't tutor someone in specialist maths if I'd only studied methods myself, likewise I wouldn't pay for tuition from a company which up until very recently was in no way targeted towards the ucat.
However, having already gotten into university I'm not exactly thinking about ucat/UMAT anymore so it's possible that these companies really have put significant time into making their courses as detailed and helpful as possible. In that case, maybe someone who has experience with both will be more helpful