@Blur to answer your questions:
The advancements over the last 4-5 years have been exciting, but they are not perfect. No business should ever offer you 100% without a shadow of a doubt full tattoo removal. Too many variables from getting a tattoo done to your immune system will play a role. It's not just a quality laser and a trained tech.
We call it ghosting but yes, in any full removal situation I always explain on day 1 there may be trace amounts of pigment left.
While it's unlikely for this to happen, being treated by a non-FDA approved laser, or by someone who isn't qualified, or by not following the aftercare and picking / poking / prodding it is possible to scar yourself.
Yes, hyper and hypo-pigmentation are a possibility and should be discussed prior to starting treatment after a skin evaluation has been done.
Laser tattoo removal is the most efficient with the least amount side effects when compared to the other more invasive methods of tattoo removal. There is no best laser though. It's the right tool for the job, just like the best tattoo machine can't give you the best tattoo.