I wear a bit of g-star. Attacc low is similar to Thavar. 3301 straight is similar enough to Safado. The tapered cuts are quite loose in the thigh and very narrow in the hem so i never bother with them. The quality is quite good sometimes but like all brands you get what you pay for and the denim is reasonably priced but the washes lack detail. My all time favourite pair of denim is my attacc low in coal. Ive had them for years and they have never stretched at all even though the denim is quite soft and thin. Oh and always size up one from your Thavar size as the upper block is quite slim.
Where G-Star really shines in the jackets. They are exquisite. Such craftsmanship and always loaded with cool details.