Has anyone on here used it and do they rate it?

Reason being I was chatting to my brother about stone chipping the floor as it's all new and leaving it black as it's easier to maintain, the painted floors all chipped already and it hasn't gone anywhere but leaving the arches body coloured as you can see them. My brother said he has some black 3M stonechip and gave me 2 full tins and one tin with just a bit left. I put this bit on, only a thinnish layer on the back then realised it's the non over paintable bitumen stuff. Now I'm wondering if this stuff gives enough protection as the rubberised over-paintable version?

I sprayed all the new bare metal with a layer of cold galv zinc spray and sealed all the seams with Tiger Seal but I can't help but think it needs more paint under the underseal?

Am I being paranoid? Or should I start again?