Walkers have been dubbed by several people as the most overpowered skill in NeoLemmix, due to their versatility. Too many advanced puzzles revolve around questions such as limiting the number of times a given lemming can turn around, or how a Blocker can be freed, and the Walker takes care of both.
Shimmiers, in contrast, can cancel skills - but not Blockers - without having the additional potential of easily turning lemmings around either. Of course, depending on the structure and position of certain ceilings, they can introduce other backgrounds that Walkers couldn't. But so far, a regular, shimmiable ceiling appearing by accident seems to be the exception rathe than the rule.
What's you experience on this so far? Have you been using Shimmiers as a mere cancel skill instead of Walkers?
Maybe it's also easier to hide the availability of such solutions, because this option is still less familiar to people at the moment, whereas for Walkerrs, canceling skills is one of their main intended uses.