l'll give my tuppence worth here, l have used Scratch X many many moons ago,it can be pretty severe even with medium pressure applied by hand ie it will remove the scratch but it will also dull your clear coat at the same time,so you'll then have to use another polish to bring back the clear coat,as for Ultimate compound l dont have any experience with it,but what l will say is fool proof,any one stage correction compound will remove any marks on the clear coat easily and with no risk,l've had 2 members PM me on here asking what should l use to remove
1.Bird Poo Etchings
2,Scratches on the clear coat
they never had a machine polisher,they just bought some microfibre pads and removed their paint dilemmas with the same one stage compounds as ls used with the DA/Rotary
Scholl S20 Black or the Sonax profiline perfect finish will give outstanding results by hand with no risk of dulling your clear coat as they have diminishing abrasive tech...ie they correct firstly..... the larger abrasive shaves the clear coat then its the smaller abrasive turn to refine the clear coat thats been shaved off to get rid of the scratches or marks
Stay away from The Halfords mentality guys,just because you dont fancy using a machine polisher does'nt mean you cant use the 1 stage compounds or polishes you can use with a machine