I don't rate Gtechniq as very good. I put the their best products at the time on when I had my car new ready and prepped, and and ended having to remove everything and go with a different brand that actually worked. Adam's Polishes is also another brand I would stay away from - cheap and doesn't perform.
I would recommend the following brands: CarProUK, GEYON, ArtDeShine, Ethos Car Care (USA based). SOFT 99 also have some good products.