I have had both this year and to me the permagreen does better with the granulars than the zspray. It has better control of where the granulars are going. The Z just slings it out there. You will get more product on the road, sidewalks, and in the swimming pools; even when using the deflector.
The Z however does a better job when putting down the liquids. There is not even a comparison.
The Z is much faster on large areas and the same on small areas. What you have to look at is the cost. If you are buying new no matter what, then the Z is the way to go. But you really cant beat a used permagreen centri for around $1800. You really need a lot of square footage (acres) to justify the Z. I Guarentee you that the $8500 that you think the Z cost will be more like $9500 by the time you add all of the extras that are great and that you DO need on the Z