I’ve got
/repositories/KDE:/KDE4:/Factory:/Extra-Apps/openSUSE_Factory
which has 1.9.95.10-21.1
do you mean I should have
/repositories/KDE:/KDE4:/Factory:/Extra-Apps/openSUSE_11.0
which has 1.9.95.10-21.2
Can I use both of these repositories simultaneously?
They are two version of a single repository. The first one is the version for openSUSE Factory (development version) and the second one is the version for openSUSE 11.0.
If you are using Factory use the first one, if you are using 11.0 use the second one.
All Build Service repos are the same, the last part of the URL specifies the openSUSE version.
NEVER mix repos from different openSUSE versions.