2008 taco sport long bed strut spacers

Just bought a 2008 tacoma trd sport 15k miles with the long bed. was wondering if those strut spacers that go between the truck and the strut are safe and worth while....I have seen them on ebay for under 100bucks, I think they call it a (leveling kit)

I planned to put the 3" leveling kit on the front and a 3" add a leaf in the back. It just seems too easy to get 3" that way....if so great I would just like to hear from some ppl that maybe have done this .

thanks any advice would be great help.