My first rule of good mechanical work is to use the simplest tool for the job.
For cutting bars, stems and seatposts, that would be a hacksaw.
A simple guide can be made with one or two hose clamps.
The case against pipe cutters is simple,it's the wrong tool for the job.
1 in the size range needed it's costlier than a saw.
2 pipe cutters are for soft materials that flow easily. Heat treated steels and aluminum alloys aren't.
3 pipe cutters roll a large burr to the inside, and raise a smaller one on the OD, so there's more clean up work needed.
4 with a modicum of skill, a saw raises a small burr which files off easily.
FWIW pro bike mechanics used hacksaws for a century, but as culture evolved, folks started doing more DIY, and eventually word got out that it was easier to buy a pipe cutter than to learn to cut straight with a saw.
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