L2OFF Interludes files are more complete and stable than L2j in many aspects, they are not that difficult to install if you have a decent guide. :)
The free ones are just "okay", meaning they have problems and some game mechanics are not working (like global freight) but I would say they are 80% complete; the quests and epic bosses are working as they should, skills are working well as is the normal retail mob spawning system in addition to most game mechanics.
The paid L2OFF Interlude files are much better, about 98% complete but run between 200 and 300 US depending on the seller.
If I have some free time I will set a server up using L2OFF IL and let you test it for yourself.