There may be a small performance penalty using qef. The overhead of running lclvrs, sls, qsg, and qefpp() is not negligible but not excessive -- less than a second per directory on a 486, sgi, sparc, or rs6000. But many of the scripts and tools use techniques to avoid gratuitous time stamp propagation, thus in many situations qef avoids work that other systems would perform. Furthermore, the parallel process facility and other features actually reduce the build cycle time. One site that audits build cycle times reported a 66% reduction in the time taken to build their product.
Gaining acceptance from developers is sometimes difficult due to their resistance to change and their suspicion of radically different or novel approaches. Furthermore, a lot of the problems qef solves are problems that do not concern programmers or ones that they don't believe they hav e. There was a similar resistance to make initially. However, when challenged on programmer acceptance of qef, the author asked a user how he would feel about going back to using make. His reply was that it would be similar to going back to DOS.
One of the necessary characteristics for a construction system that was listed in the first section was that the system needed to be simple. make is fairly simple in its syntax and semantics, but the make files themselves and the actual use of make to control large scale projects can be exceedingly complex. qef uses a collection of small languages which may make it seem complicated. Indeed, qef's processing is complex, but its complexity is largely hidden from its users. The greatest difficulty in promoting qef is presenting it to an audience that currently uses make. Programmers are notoriously reactionary and resistant to change. They expect to understand qef sufficiently to deal with complex problems in the first ten minutes and forget how long it took them to achieve a similar understanding of make. qef is a complex system, although the individual components are simple and the qeffiles are invariably tiny. The complexity lies in their combination to achieve the other requirements.