Remember, if you get yourself a cordless grinder you will have to buy the body, batteries and charger. It makes sense if you stick with what make you already have for your other cordless tools.
I personally like and rate Makita and I took the plunge last year with buying the grinder, impact driver, drill, batteries, charger and box (although the box came with the drills). I also bought the vacuum, but I would not recommend it.