Looks to be very well made... and quite attractive, if you're into the "attractiveness" of Glock stuff.
2.9 oz. added to a Glock, all things considered, isn't too much to worry about for anything other than perhaps a CC gun.
Is most of the additional weight via the use of the "Seattle Slug"? If so, then you can, if they make the option for the Gen 4
, add even more weight with the heavy slug.