People recommend it for many reason...either they have one, or have one and are sponsered, or do it because thats what everyone else says...however, the truth lies in your personal circumstances.
What do you want from a marker?
What can you afford for a marker?
If teh answers are:
As much as possible.
Not a great deal.
Then the Ion is teh best bet...
There are better guns out there, but will cost you more.
Buy one secondhand, maybe with a trigger an dfeedneck on it and your sorted...if you can afford to spend more, then do so.
I personally amd not a SP fan, but teh Ion and Shocker are both very good markers.