If you have an apex jr, have you used all 5 modules permitted on the aquabus? If you have less than the 5 you are permitted, go ahead and get the WXM module now. You will need it no matter which apex you get.
I just have mine opposing.....the one runs in reefcrest, the other in antisync.
Don't put it too close to the rock...if you ever put anything on that rock, it will get beat to heck from the current