Same idea as the construct your own lightsaber product that came out not so long ago. You have components to form 3 different sonic screwdrivers, one being the current 11th Doctor's model, though the prongs don't spring out.
They divide into 4 sections consisting of emmiter, control section, grip and base. The internal battery core and light slots into the grip, though it can take a little bit of force, and the control section slides on top and clicks into place. It can be a little bit awkward and stiff so younger Doctors might need a bit of help to prevent breaking it.
Once built though they feel sturdy enough and look really good. Apparently you can get 80 different combinations, though it doesn't feel like it. I originally thought it just made the usual sonic sound, but it turns out multiple rapid presses of the button results in 8 different sounds.
It's a great set, can imagine young fans will love having their own favourite sonic combination and I'm sure a few older fans will be getting it out of the box on more than one occasion.