Have to agree with Tonks on the stats issue - if you succeed then 100% of you have got in, if you don't it's 0% - if you want it then goferit.
You can keep your options open anyway. When I wanted to join (with quite good A levels
) I applied for both Direct Entry and for University, on the principle that if one didn't come up, then the other might. In fact both did! Three really, as OASC tried to persuade me to go for "real" Cranwell, which I turned down (sorry BEags!).
Opted for DE because I had no idea then that I would still be wearing uniform (albeit occasionally!) 30-odd years later, but mostly because it got me to a squadron 3 years sooner than the Uni or Cranwell options . There are indeed many ways to skin a cat, or to achieve a satisfying military flying career.