I downloaded source package kdetoys-3.5.10 from KDE site under Download -> Stable Version and the comment: "KDE 3.5 is the more mature version of KDE. For more conservative users, this is the recommended version of KDE." But after the tarball was unpacked I read in README that this is alpha version and it is recommended to turn on debugging option with configure script. Is it stable or not indeed?
In addition, is it possible to install this package correctly in KDE 3.5.4 which I have with a clone of RHEL 5.2?
Expert evidence is highly appreciated.

It is likely that the KDE Toys package could be susceptible to a high number of bugs. Courtesy of binary / source compatability between KDE minor releases, you will be able to use the KDE 3.5.10 version on KDE 3.5.4