Can't speak for the HRS weight but had a Stillpoints
Will likely change the balance of the system sound somewhat, how exactly that manifests is a crap shoot, you won't know until you try.
I found when I ran a cart that had sparkling highs, neutral mids and tending toward lean through the bass there was a little more weight and a fuller bass presentation when using it. It helped. In other implementations and as the analogue front end became more neutral with greater resolution I felt it's contribution was additive, adding some weight but thickening and muddying the mids somewhat. (SP10 and Brinkmann tables)