Bottom line.
The SmartCover has the following attributes.
(1) Sleep/Wake functionality.
(2) Foldable "stand" for landscape oriented iPad
(3) Protection for the screen only
(4) Easily detachable.
There are numerous alternatives that provide the same functionality for 1 and 2. In addition, those alternatives provide protection for the back of the iPad by attaching the screen cover permanently to the back cover. What is NOT provided by any alternative is (4.) Some view that as a significant benefit. Others see it as a significant risk since it also means that one may try to pick up the iPad by the SmartCover with disastrous results. For the latter group, there are at least two alternatives for a back cover that locks the SmartCover in place (ZUM and MacAlley.) However, if one goes that route it's essentially identical to a case that includes both screen and back protection. And the price is potentially much greater.
The bottom line is that if one wants to detach the screen cover easily, the SmartCover is, AFAIK, the only option. But that benefit is balanced by some risk. If one already has a SmartCover and wants to keep it, there are numerous back covers that are "compatible" with it. But only the ZUM and MacAlley, AFAIK, "lock" the SmartCover in place.