I challenge you to try our ab workouts for 30 days ;) You would be surprised. We start with a basic fitness assessment to measure your upper body and core strength. Unless you are already starting out in the 90th percentile, you will most likely experience a 20% gain in ab strength after 30 days if you do the workouts every day. This is what the data is telling us after a year of tracking users and their results.
I'm sure it's very nice, but what I said is that I would do that in addition to my training instead of replacement! If my abs can stabilise my trunk for a 500lbs squat or a 600lbs deadlift, they're strong enough for me :)