I'm currently using Medentry (and so is everyone else I know who is preparing for this year) and it seems to be doing its job. The 2 day workshop was very useful and I couldn't ask for more in the online resources. Since I also had the group discount it didn't cost too much either.
Here is someones pros/cons from 2010 - the situations may have changed since then/you may have already read it but still.
NIE and Medentry are on par with eachother coz they both have there own strong and weak points.
NIE:
-hard copy
-24/7 help (which is good, but sumtimes there is a queue)
-Questions are decent
-I rkn there section 1 and section 2 are abit iffy in terms of question quality/difficulty compared to that of the actual UMAT.
-Section 3 is very good particularly because they give u alot of questions and plus its hardcopy so u can do it in your spare time anywhere, which why it is soo convenient, its like doin a sudoku on a train.
MedEntry:
-Online, which means its harder due to u might have to keep lookin at the screen and it gives a different feel to the situation.
-Give good answers/explanations to questions.
-Timed conditions which forces you to actually try, not coz u want to do well, but u want to get your money's worth and the tests are only on during certain times and its a one off thing.
-They grade you based on the cohort (but do not use this as an accurate predictor on how well u will do on the actual UMAT)
-The quality of questions is good in general difficulty and relevance is close to that of the UMAT
Overall both have pros and cons, if possible y dont u do both as in, if a friend does NIE and u do Medentry u can share it like the person who does NIE does it in pencil and the one doing Medentry can lend their account for the drills since u can repeat them as much as u want. Getting the best of both worlds. U can also do acer books to get a feel of the difficulty
Remember the UMAT isnt like VCE maths/science subjects u cant really study for it but u can condition your minds or gain experience through these programs. Section 3 in particular can be improved the most through alot of practice. But the other 2 sections , you can only go so far with the programs, the rest is up to your potential/understandings unfortunately.
I wish you the best of luck regarding your UMAT preparations and the exam later in the year!