Should I follow this tutorial? Unlockable lvl. screen

I can't tell you if you should use that tutorial, as that is completely 100% up to you. What I can tell you is how I would do it (and If you're confused, how to do it.) first, make the UI so that each component has a script that uses the load level command. Then, In The script check with the previous level if the level has been completed (assuming this has already been integrated) but you have to make sure the object this is attached to is an empty which will not be destroyed on level load. So when you click on it, check if the previous level has been completed and if it has load level (something) I suggest making this a variable so that you do not have to make a lot of scripts for each level. Let me know if you're confused and or if you do t know how to do one of the things I mentioned

No

Technically speaking the tutorial will work. But:

• Use sprites instead of a quads

• Consider using the 4.6 UI, its much, much simpler

• The scripts use individual variables instead of collections. This is bad

• Update is used instead of Start

• OnMouseDown is ignored

• Saving is done to player prefs

Portal 8 does have a bit of a reputation for rubbish games. If this is representative of the quality of there tutorials then its no wonder.