After becoming dissatisfied with the lack of blade control using Delta's blade guides, I tried "cool blocks".  Unfortunately, after they wore just a little, the blade wandered so much it was too difficult to accurately cut on a line.  The Carter rollers keep the blade from twisting, and as a result, cutting on a line, straight or curved, is significanly easier.  So, once the roller bearings are adjusted, they perform as advertised.  (I haven't tried 1/8" blades, where one reviewer said they don't work.)  I've had this product for several years, but I recall that it took at least 30 minutes to get all the rollers properly adjusted.  With experience that would likely go faster.  Since I mostly use the same blade, set-up time isn't important to me.