DSM Garrett t25 water lines
 

After searching I couldn't find an answer to my very simple question.

On a dsm Garrett t25, is there any downside to using a properly threaded slip on hose barb in place of banjo bolts for the water line connections on the turbo?

It's less secure and more failure prone than a banjo fitting.
Otherwise it shouldn't really matter, other than if it fails someplace 500 miles from nowhere.

i would say not to use the barbed fittings, the turbo gets really hot and would next to melt the lines causing them to crack and dry up...

Use the hard lines. They move the rubber portions well away from the heat of the manifold.

I replaced my silicone hoses with banjo fittings with AN banjo fittings and steel braided lines.