You may get results, and it's nice you do, I'm just saying that time can be better served doing a different exercise than something that solely targets the core I.E situps, crunches w.e it may be.
Because, like I said, pretty much any exercise can work your abs and core, most noticeably would be running/walking or any cardio of the sort, then the likes of bench press, pushups and squats even work your core. I personally would rather use that time doing military press, butterfly's(sometimes just call 'fly's'), triceps extensions or bicep curls or something that works your arms or back.