These things don't behave like a perfect switch, so the contact resistance actually transitions as you trigger them and it seems the actual current threshold makes a very slight difference to the accuracy but our controllers will tend to trigger at a fairly consistent threshold. These things are capable of working to 1um or better, whereas our machines would be doing well to get down to 10um. Nothing to get too focused on.

I think there may be others apart from the MP1 but TBH I never got into it much. Having said that, I suspect it's only the old models that will come up at a decent price.

For tool setting, there is the TS27R. These also come up on ebay if you are patient. I got one a couple months ago for £190. Again, you can hard wire them without the interface box.

If you dig about on the Renishaw website in the legacy support area, there are datasheets and app notes for the older models. It's worth having a poke about there so you can understand how to set them up and how they work.

https://www.renishaw.com/en/legacy-touch-probes--32452