I have a few general guidelines when it comes to deciding what to buy.
If I have to borrow it more than twice...it's time to get my own.
I try to have a different brand or model than everyone else...makes it harder for them to get mixed up.
When trying out a new type of tool, I will usually get a cheap import POS....just to see if the thing is worth having. If the concept prooves out, I get a quality version. Thenh the POS is relegated to home/ spare/ lending use.
I'm not averse to making (or modifying) tools to suit my specific work.
As far as power tools are concerned, there is a lot to be said for trying to get tools which use the same charger (good) or batttery (better). For this to work, you need to anticipate your future tool needs- will you really need that cordless angle grinder? What about a small vacuum?
Be extremely wary of marketing hype.....some of those Madison Avenue types are so slick, they can give an Eskimo the urge to run out and buy the "new and improved" snow! Some of this is blatant....as in ads, while some is quite subtle. There is a reason everything at Sears is shiny, and wrapped so nice!
I also play down any kind of "brand loyalty." Often a company will have an excellent tool...as well as a mediocre tool....and a piece of junk!