For such a small amount of work, a mechanical tool is unnecessary and will cause far too much dust.
After marking your cut lines on the wall, you can use a club hammer and a bolster to gradually cut into the lines, and the plaster between will fall out.
Here's one from many years ago.
As far as I remember, it was 20mm oval conduit with 16mm cable clips to hold it pending plastering, but pulled out once hard.
This was in a region where walls were traditionally rendered with sand and cement (sand and lime in the old days) with a hard finish plaster skim. I find that very easy to do.
After marking your cut lines on the wall, you can use a club hammer and a bolster to gradually cut into the lines, and the plaster between will fall out.
Here's one from many years ago.
As far as I remember, it was 20mm oval conduit with 16mm cable clips to hold it pending plastering, but pulled out once hard.
This was in a region where walls were traditionally rendered with sand and cement (sand and lime in the old days) with a hard finish plaster skim. I find that very easy to do.