hope it goes ok. all mine have and have also had free bring label and pick up from royal mail, which is great as they are back to charging 30p now. But that system failed the first time my mother sold and we tried free collection - there seemed to have been some glitches.
Did you use tracked royal mail before SD? If you did then SD now seems to be cheaper for small parcels so any addition in sale price should be covered. I'm only signed up for Royal Mail as Evri drop off is fair distance away. At first the SD prices were higher than RM but that has been adjusted now.

I've always done tracked 48 for everything over £20 and kept it as RM cost.