For the first part of the question:
The community is comparatively small (at the time of
writing, the software is less than a year old), but desklets
writers are competent and generally dilligent.
As for performance, adesklets is generally heavier than
GKrellM, but in my experience many order of magnitude lighter
than gDesklets or SuperKaramba -- this is just qualitative,
but adesklets runs smoothly on an 1993 Pentium, but not the
two others. Performance was not the main incentive for
writing adesklets, but only a consequence of not being
dependent of such a large amount of external code (not to
mention that Imlib2 is really fast).
Of course, performance should probably not be the only
criteria: free software is about
choice; adesklets is merely one more.