I am not yet a Taxi member. But from everything I have seen and read and watched, I am convinced they are an organization that helps songwriters get better and helps those that are great to get deals! I do not know how much help you can get nor do I know if it is significantly easier to "break in" using a different service (or none at all).
But I have been quite impressed with the high quality of the songwriting and production I have seen on the Taxi forums. So, one way they help immediately is to expose you to a standard that may be well above what you are used to! Furthermore, the songs I have reviewed at Taxi tend to be more modern than you might hear in certain software forums!

My interest in songwriting is mostly as a hobby. I am interested in getting my songs as nice as they can be but I have little to no interest in trying to pitch songs. So, I may or may not join Taxi some day!