If you want to use it with text fields this is the developer reponse:
"You need to use k2 extrafields with pre-defined values (not text) for
working fine with slider and other not text search fields (drop-down)."
So DOES NOT SUPPORT IT. This is not in the extension information before purchase it.
But the most dangerous thing is that if you use it with 6+ extrafields (in my case) then the native K2 finder plugin cannot reindex the K2 items when creating/editing and YOU CANNOT SAVE K2 ITEMS ANYMORE because the script execution time exceeds the default 30 seconds.
You have to disable the finder plugin, decrease the extrafields used in the module or modify your server configuration to increase the script execution time.
That REALLY RELEVANT INFORMATION wasn't also in the extension info. Breaking the K2 functionallity isn't enough relevant to warn users...
The support answered the email 48h after reporting the issue. So after spending my money I had also to spend my time debugging it to solve the K2 issue and keep my site working.
In fact, the problem is that you do not want all to understand better.
1) Work with text fields
It is support it, but it is needed easy manual adjustments.
2) "YOU CANNOT SAVE K2 ITEMS ANYMORE"
This issue can not be associated with this extension, because the module and plugin part does not affect to K2 functionality in save/edit items.