No.
HK G3's are full auto military battle rifles. The HK 91 is the semi-auto version of the same.
The HK G3's that are being advertised are old full auto parts kits built on US made receivers (either Speshul Wempons, Century, Hesse, or Fed. Ord.). The worst of the bunch are the aluminum receiver guns, followed by the others (all of which are basically bottom of the barrel).
A real HK 91 will cost about $2000. The only "clones" that are worth much are the FMP (imported Portuguese contract receivers) based guns built by professional gunsmiths like Pro-Tech. They generally run about $1000. The SAR-8 aluminum receiver guns are a little better quality than the Century guns (basically all the earlier mentioned clones, regardless of the receiver are Century guns), but I would still hesitate to get an aluminum receiver gun with that particular design. There are some imports that are pre-ban or post-pre ban (i.e. they were imported with thumbholes) that are pretty good--the earlier SAR-3 or SAR-8 Greek made guns (the -8 is a later import with the thumbhole, but both are HK contract guns, and of good quality on a steel receiver), there were a few factory Portuguese guns imported, and the HK SR-9 series, and the 911's, but generally they run almost as much as a pre-ban HK 91.