I've used many versions of the exercise wheel over the years, some had springs to help out others had four wheels to prevent you falling over, but this original version is by far the best. But be warned, don't try to do more than three or four repeats for the first week or so. It's very hard on the abs and you could quite easily do yourself a mischief and throw the thing away in disgust and miss out on a great stomach and abs workout.
It can get quite addictive, I bought this version because it was light enough to pack and take on holiday so I don't have to miss out on my daily workout. Excellent value for money and a great product.