WD40 is good for free seized parts and cleaning and that's about it, it is not much of a rust preventer or lubricant, it just sort of vanishes.

Boesheild is sort of waxy so I have also read people complain about it, I would not use it on a table saw top because you run wood on it but on a machine tool it is good to protect everything that is not already lubricated, it's especially good when you put something away in storage or for parts that are hard to oil.

Not sure about putting it on collets, you can have oil on collets so I don't see why not.

Graham