I bought it to replace the old one which, due to limescale, did not fit well and was leaking water.
For the installation, the base also had to be changed so the whole cistern had to be removed.
For its own base, it includes a wrench, but for the old base I hadn't kept it and I struggled a bit to remove it.
I also changed the screws that hold the cistern to the toilet bowl. The old ones were better but if you remove them their rubber gaskets get damaged and you can't reuse them, so I used the new ones.
It has instructions for adjusting it (for more or less water), they are not very easy but if you spend a little time you'll understand them.
The (dual) button screws itself onto the lid. Underneath, it has 2 plastic screws that you can unscrew and cut to the right length so they touch the mechanism exactly. Essentially, this is the only 'modification' you need to make, the rest is simple assembly.