The kit arrived promptly and went together very easily, providing you follow the instructions which are very clear. The cardboard sheet is to ensure it's true when you glue it and the chipboard sheet protects the surfaces. The add-on kit gives you the glue, sandpaper and tapes to tension the glued joints. The glue is very good and strong and gives you time to adjust the parts - but don't hang about because it dries fairly quickly.
I'm sure the tapes work fine but I used clamps because I had them available. All-in-all everything is there to make construction easy and good quality and I'm very pleased with the result. This little add-on kit is well thought out so you don't need a workshop and the only tools you need are a hammer and a means of cutting the hole in the back.