Ab Rollers can definitely have a part in a fitness and weight loss regime, just don't expect too much of them. There are many ab roller/cruncher designs out there, but they don't have a good reputation as these have long been the favourites of late night infomercials. That said, most of these designs will help you to do perfect form crunches and work your abdominals, but this should be just one stage of your workout, perhaps five minutes of crunches following an aerobic DVD workout or crosstrainer ride.
Ab rollers / crunchers are designed to improve your stomach muscles as you perform various sit-up type exercises. The advantage of having a roller means you will stay in perfect form throughout the range of motion and will support your head, avoiding pressure on your back and neck so common with garden variety sit-ups. One of our reviewers had done sit-ups nightly as a teenager with good results, but disliked the neck strain, which is something the support of these machines alleviate.
There are some very cheap Ab Rollers/Cruncher around, but we found the best value was the Carl Lewis Ab Roller which includes a workout DVD, and also a mat for comfort, which most units do not. Perhaps as important, you can pick on up for about half the retail price on Amazon. The Carl Lewis Ab Roller can be easily assembled and is solid, yet also light and easy to move around. There are several exercises, including a basic crunch, side crunch, and lower ab crunch.
The mat is the only part of this ensemble that lets it down--certainly not yoga matt quality, and it is a bit thin. Still, if you're on carpet you won't need it anyway, and if you're on a hard floor, you'll really want to buy a quality yoga mat separately. The unit is designed for individuals up to 100 kg (~15 and a half stone).
The Carl Lewis brand is a trusted and effective range which is part of the Alba Plc electronics group. You can buy an assortment of Carl Lewis products, from horse riders to abs crunches, and most are very highly rated and reliable. The treadmill is named for the athlete who won 10 Olympic medals and 10 World Championship medals.
Prices: The Carl Lewis Ab Roller DVD retails for £39.99, but you can get it much cheaper on Amazon for around half that at £19.99, a real bargain.