I have a partially blocked toilet and have tried unblocking it by hand, with hot water from a height, and Kil-Block drain unblocker. The next step would be to try One-Shot drain unblocker which is extremely powerful. But I am worried what it's effects will be on the piping coming from my toilet as it is plastic

Do you know where the block is ? Would running a snake though the pipe not be a option in there somewhere.

I am no fan of putting harsh chemicals in your drainage system. For me there's only one way to unclog a toilet and that's with a closet auger,( see image). Purchase one and forget about chemicals that only seem to work in TV ads, Good luck, Tom