There is currently no way to identify most libraries and instruments that will load without limitation in full Kontakt 5.8.1 (before you download them), this should help.
Any that show as a Kontakt download but are not in this list will require the full Kontakt 6 to work.
Kontakt Player is essentially a trial version, allowing you 15 minutes use until you need to relaunch Kontakt.
The 50 instruments that come free with the NI Kontakt Player download will not time out and there are also some commercial libraries that won’t time out either.
Due to the absence of editing and the limitations of posting on this site this list might seem a little cumbersome but it is all there is at the moment.
Finally, anyone who has the full version of Kontakt 5 can fix it to load exs files, with some degree of success.
Converting Kontakt 6 Patches to Kontakt 5, EXS to Kontakt