Octagonal violin bows such as this great student Primavera bow are often preferred by those who like a little bit of weight to their bow.
All violin bows infact start off octagonal, and the archetier (bow maker) will then keep some sticks octagonal, whilst rounding the others off.

There is no proven advantage or disadvantage to using an octagonal bow, it really comes down to personal preference, but octagonal bows will often be ever so slightly heavier than round stick bows.

This Primavera Octagonal Violin Bow is crafted from hardwood for the stick, but includes a fine ebony frog as opposed to a cheaper rosewood or even plastic frog as still found on some entry-level bows.
Ebony is a delicate and impressive wood that feels comfortable to hold and is nicely weighted. A pearl-eye dot is featured along with nickel silver half-mounting, whilst the lapping on the stick is copper-nickel.

A popular choice with beginners and entry-level players in their mid-teens and above, this bow is available in a range of sizes from 4/4 (full-size) downwards to cater for all size violins bar 1/10 and 1/32.