Do you mean the proprietary Apple push notifications in Safari? In this case I've only seen it ever once (as opposed to seeing the "normal" notifications on pretty much every shitty blogspam website) so it seems like the 100$ acts like a good filter against BS notifications.
I mean whatever Firefox does. I’ve never once gotten spam because sites can’t send you notifications unless you opt into them (so it’s more like a battery friendly super fast RSS replacement.)
On the iPhone they require paying apple $100 a year which almost ensures most will be ads.