Hi Stamitis
The G-Techniq products are very, very good.
I didn't use the P1 polish on the roof arches as the polish does have cutting ability and as there were no marks or scratches on them I didn't feel it was needed. Instead I used a polish which does not have a cutting ability but it is a deep cleanser and it brought the arches up really nicely. If you were to be careful, it should be okay using the P1 on the arches by hand. I wouldn't personally use a machine to polish them. I just don't know how much paint the arches have on them so it's best to be very very careful.
I have since used P1 on the roof to remove a few light swirls, when I did my Spring detail in March and I had no problems. It removed them easily. The cutting ability of P1 is dependent on the pad used (by machine polishing) so hand polishing will remove light marks but won't be too aggressive.
Did you get the C2 sealant? I have that on my roof. Do you intend to use it on your paintwork. It gets great reviews and lasts up to 8 months.
The G1 on the windscreen is absolutely awesome, the best product ever :thumbup: