Hi Biy,
If you are really serious about the UMAT, then just do your own research and don't go around asking if UMAT prep helps or not. Different people will tell you differently, i.e. those that prepared and got into med will say - yes do the preparation, those who prepared an did not get in obviously will say don't study. A lot of students just want to give it their best shot and don't leave anything to chance, and hence do quite a bit of preparation. Remember, familiarising yourself with styles of questions, and practicing trial test papers to get the hang of what you are good at and which areas you struggle with, etc etc all adds up to your exam-readiness. So have a look what preparation is available to you, and decide what will work best for you.
Some UMAT prep organisations have online chat services where you can just go and talk to someone online and tell them what you need help with and ask for advice and to what is the best method of preparation for you. Students from my school often use either this website to ask questions or there is another one called 'NIE', their online chat or over the phone service is pretty good, my students use it fairly often. We like them because they don't try to sell you anything, and will actually provide you with pretty good advice as to what you need to do to prepare for the test. Another good link we recently received in our school, which I think is great for anyone aspiring to be a docotr is
http://www.myhealthcareer.com.au. It really shows you what career in med is about, has a lot of useful links on there and has a very good unbiased article about UMAT and GAMSAT prep.
I hope this helps, Good luck!