Just a word of caution, it's not recommended to put claning blocks into dual flush cisterns.
The chemicals in them can degrade the rubber flush seals quite quickly.

a straightforward task for most DIY enthusiasts
Well that's frightened me off. My nickname is Mr Bean.
I think some are screw ones.
The following was included in one of the writeups for a top flush mech ........
Easy installation: With a 48mm diameter suitable for standard cistern holes, this push button simply screws into the flush valve, making replacement a straightforward task for most DIY enthusiasts