I have used free weights for over 20 years now...I gave that ab roller a try ...the one where your stretch out in front of it and all the pressure is on the abs...its actually a decent piece of equipment and the exercise has a nice feel to it....
I would recommend that one...for anyone wanting to add an exercise to his routine.
By the way, if you only pay 19$ a month, you will be paying on it for about the next 30 years. Its a revolving payment plan like paying the min on a credit card.