What are the ethical issues at stake when companies permit employees to use personal technology on the job? what are tge implications?

You'd sure find out under strike conditions or if an employee (you) quit or were fired.

The main thing is all the material (for example) stored on your computer would not be able to be confiscated. This happened in our school district when we went on strike. The board could and did confiscate our day books because they had issued them. That was OK with me. Mine were written in a jcherry99 code that made perfect sense to me, but I defy anyone else to figure it out.

What about tools? If you are building a house and the tools are yours, and you break a very expensive one, is the employer liable to replace it? Why would he be?

There must be all kinds of safety issues. You're using a tool of yours that you neglected to tighten a bolt that holds a saw blade in place. Of course you were in a hurry but a board needed a cut that only you could do. The blade comes off luckily only giving you a cut. But you have to go to the hospital to get it stitched. Should you lose time? Who is responsible? It's even tricky if the company agrees to rent the tool from you.

These are a couple of reasons why people work under contracts. It protects both parties.