Whilst being the most expensive option for a set of extension tubes I feel comfortable that the product is well made and fits snugly on the camera and lens.
I have used it, so far, with a 105mm f2.0 prime lens and a 200m zoom and have some satisfying results. Contrary to claims the autofocus function, even in bright illumination, does not work effectively or at all.
This is not a huge disadvantage as for most practical situations the use of manual focus is preferable in order to cope with the very limited focus range and to select the preferred centre of maximum sharpness.
In my opinion this purchase is probably the best cost/quality effective way of entering a serious attempt at 'macro' photography and the price justified vs. some of the cheaper, less well engineered alternatives.