Instant reload - Double Barrel Shotgun calculation - Worth?

TL'DR: It increased DPS by aroound 23%

I did a little experiment.
Using Shotgun with double barrel I've shot 10 shots.
Before and after investing skill points into Instand reload and two previous nodes.
Before it took around 10,7s
After it took around 8,7s
It's a DPS increase of around 23%

BUT because there is a gem spot before those nodes, I still think this can be a good place to invest your skill points, especially if you would be close for others.