For grouse and rabbits. RST sells them and cabela's has Herters brand sometimes. Opens up your patterns better for close range shots so you don't mangle them. I'll use a spreader for the first shot followed by a regular shell(s) for the assumed follow up.
You can make your own if you reload. Just cut off the petals from the wad. I used them that way for grouse and woodcock. Don't like them for rabbits especially when using a dog unless it's really thick cover. Works great for doves when they are flying close.
I shot fiochis in my Winchester M50 12ga for small game..mostly grouse...the gun has a 30" full choked barrel and patterns like it...with the spreaderload it's probably improved cylinder..maybe light mod..
Worked great...a spreader load of 8s dropped me many grouse...