I've used em they seem ok. The only problem I have with abs in general is everybody claims to have the quick and easy solution ( 5 Min abs ) and stuff like that. Being prior military I pretty much stick with crunches and side crunches for my obliques but I have also been blessed with a good mid-section. The only sit-ups I do lately is to get my a*s outta bed to go to work but I still have a pretty nice six pack. One exercise I learned about 16yrs ago are hanging upside down sit-ups with
gravity boots on. I used someone on that exercise to keep me from rocking back and forth like a pendulum. I do use other exercises when I care about my abs but from your your avatar pic I think you got the bases covered.