How is Pam's Song and Shielding Scroll different?

So I found out about the renegades farming trick for 20% scrolls and I want to scroll some stuff.
Before I do any of that what is the difference between Pam's Song and Shielding Scroll?

I believe with pam's songs, if the scroll works, the effect stays until one fails. With shield scrolls, even if the scroll works, the effect of the shield disappears.

Shield scrolls are used before scrolling. You put the shield on the item, and then you use whatever scroll you wanted. Regardless of whether the scroll fails or succeeds, the shield gets used up. You need another shield if you want to try another scroll.

Pam's Song is used after scrolling. If you attempt to scroll something and it fails (but doesn't blow up), and you have a Pam's Song in your inventory, a dialog pops up asking whether you want Pam to sing a song and restore the lost slot to the item. If you choose not to, or if your scroll succeeds, Pam's Song does not get used up.

For all purposes i believe a shielding scroll its basically a white scroll you can buy with nx?

Shield scrolls are used before scrolling. You put the shield on the item, and then you use whatever scroll you wanted. Regardless of whether the scroll fails or succeeds, the shield gets used up. You need another shield if you want to try another scroll.

Pam's Song is used after scrolling. If you attempt to scroll something and it fails (but doesn't blow up), and you have a Pam's Song in your inventory, a dialog pops up asking whether you want Pam to sing a song and restore the lost slot to the item. If you choose not to, or if your scroll succeeds, Pam's Song does not get used up.

Can both Pam's Song be used in conjunction with 1) whatever it was that saved your scroll if it failed Guardian Scrolls and 2) wards?

For all purposes i believe a shielding scroll its basically a white scroll you can buy with nx?

seeing how WS at scania FM is about 140m-150m (with the NX rate of 1:50m) its much cheaper to go with the Shield scroll bundles (11 of them)
that is of course until they remove the discount
Most merchants are noticing this and started selling WS at 80m
if you are lucky enough its still going on now at FM