Hi!
I have tried water-slide decal paper around three years ago. You don't want to use inkjet paper, because the decals need to be sprayed before immersing and they look awful then.
Laser water-slide decal paper is good, providing you have your own laser printer. In print shops they won't use a paper they don't provide most of the time, for the reasons Gordon mentioned.
Even though I convinced one guy to try the laser paper I'd bought, the result was disappointing. That was because the files I had were Photoshop files and he had to convert them to .jpg, with a mandatory change of colours.
Above all, water slide decals are clear (transparent), so you can only apply them upon plain white parts.
Hope this helps,
A.